Serotonin-melatonin interactions in acetaminophen and N,N-dimethylformamide toxicity
- Anoopkumar-Dukie, Shailendra
- Authors: Anoopkumar-Dukie, Shailendra
- Date: 2000
- Subjects: Serotonin , Acetaminophen , Melatonin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3898 , http://hdl.handle.net/10962/d1003957 , Serotonin , Acetaminophen , Melatonin
- Description: Acetaminophen and N,N-dimethylformamide (DMF) are compounds which are extremely toxic to the liver. Acetaminophen is a drug which is well known for its analgesic and antipyretic properties. However, the abuse potential of this agent as a non-narcotic analgesic in alcoholics is well known. It is also the leading cause of overdose in England. DMF toxicity results mainly from occupational exposure. At present there are no known reports of an antidote for DMF poisoning, while N-acetylcysteine, the antidote for acetaminophen poisoning, is known to produce adverse effects. The present study evaluates the potential of melatonin as an antidote for acetaminophen and DMF poisoning. This study also investigates the mechanism underlying acetaminophen addiction and abuse. Initial studies involved in vitro techniques in an attempt to remove the complexities of organ interactions. The photodegradation studies, using ultraviolet (UV) light, revealed that melatonin accelerates the rate of acetaminophen degradation in the presence of air, and reduces the rate of degradation in the presence of nitrogen. This study also revealed that melatonin is rapidly degraded in the presence of air, following UV irradiation. The effect of DMF on hydroxyl radical generation was also determined. DMF was shown to act as a free radical scavenger, rather that a generator of free radicals. The in vitro studies were followed by lipid peroxidation determination. DMF (0.4ml/kg and 0.8ml/kg) did not produce any significant increases in lipid peroxidation in the liver. Three different doses of acetaminophen (30mg/kg, 100mg/kg, and 500mg/kg) were administered to rats for seven days. Acetaminophen (500mg/kg) was shown to significantly increase (p<0.05) lipid peroxidation in the liver. Melatonin (2.5mg/kg) was not able to significantly reduce the damage. The lower doses of acetaminophen (30mg/kg and 100mg/kg) did not increase lipid peroxidation. Electron microscopy studies showed that DMF adversely affects the liver, and in particular, the endoplasmic reticulum. Co administration of melatonin (2.5mg/kg) was able to reduce the damage. Further experiments need to be performed before an accurate assessment can be made on the ability of melatonin as an antidote for DMF and acetaminophen poisoning. Several experiments were done in an attempt to uncover the biochemical mechanism underlying acetaminophen addiction and abuse. The first experiment targeted the liver enzyme tryptophan-2,3-dioxygenase (TDO). This enzyme is the major determinant of tryptophan levels in vivo. Acetaminophen administration (100mg/kg for three hours) was shown to significantly inhibit (p<0.05) the activity of TDO, indicating increased peripheral levels of tryptophan. This experiment was followed up with determination of brain serotonin and pineal melatonin. Brain serotonin was determined using the ELISA technique. Melatonin was estimated using this technique as well as with pineal organ culture. Acetaminophen administration (100mg/kg for three hours) significantly increased (p<0.05) brain serotonin levels. Using organ culture where exogenous (3H) tryptophan is metabolised to (3H) melatonin, acetaminophen (100mg/kg for three hours) was shown to significantly increase (p<0.05) pineal melatonin concentrations. However, the ELISA technique did not reveal any changes in endogenous pineal melatonin levels. The final experiment was the determination of urinary 5-hydroxyindole acetic acid (5- HIAA), the major metabolite of serotonin, following acetaminophen administration (100mg/kg for three hours). Acetaminophen was shown to significantly reduce 5-HIAA levels (p<0.05) suggesting reduced catabolism of serotonin. The findings of this study indicate that acetaminophen mimics the actions of an antidepressant. This compelling finding has important clinical implications, and needs to be examined further.
- Full Text:
- Date Issued: 2000
- Authors: Anoopkumar-Dukie, Shailendra
- Date: 2000
- Subjects: Serotonin , Acetaminophen , Melatonin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3898 , http://hdl.handle.net/10962/d1003957 , Serotonin , Acetaminophen , Melatonin
- Description: Acetaminophen and N,N-dimethylformamide (DMF) are compounds which are extremely toxic to the liver. Acetaminophen is a drug which is well known for its analgesic and antipyretic properties. However, the abuse potential of this agent as a non-narcotic analgesic in alcoholics is well known. It is also the leading cause of overdose in England. DMF toxicity results mainly from occupational exposure. At present there are no known reports of an antidote for DMF poisoning, while N-acetylcysteine, the antidote for acetaminophen poisoning, is known to produce adverse effects. The present study evaluates the potential of melatonin as an antidote for acetaminophen and DMF poisoning. This study also investigates the mechanism underlying acetaminophen addiction and abuse. Initial studies involved in vitro techniques in an attempt to remove the complexities of organ interactions. The photodegradation studies, using ultraviolet (UV) light, revealed that melatonin accelerates the rate of acetaminophen degradation in the presence of air, and reduces the rate of degradation in the presence of nitrogen. This study also revealed that melatonin is rapidly degraded in the presence of air, following UV irradiation. The effect of DMF on hydroxyl radical generation was also determined. DMF was shown to act as a free radical scavenger, rather that a generator of free radicals. The in vitro studies were followed by lipid peroxidation determination. DMF (0.4ml/kg and 0.8ml/kg) did not produce any significant increases in lipid peroxidation in the liver. Three different doses of acetaminophen (30mg/kg, 100mg/kg, and 500mg/kg) were administered to rats for seven days. Acetaminophen (500mg/kg) was shown to significantly increase (p<0.05) lipid peroxidation in the liver. Melatonin (2.5mg/kg) was not able to significantly reduce the damage. The lower doses of acetaminophen (30mg/kg and 100mg/kg) did not increase lipid peroxidation. Electron microscopy studies showed that DMF adversely affects the liver, and in particular, the endoplasmic reticulum. Co administration of melatonin (2.5mg/kg) was able to reduce the damage. Further experiments need to be performed before an accurate assessment can be made on the ability of melatonin as an antidote for DMF and acetaminophen poisoning. Several experiments were done in an attempt to uncover the biochemical mechanism underlying acetaminophen addiction and abuse. The first experiment targeted the liver enzyme tryptophan-2,3-dioxygenase (TDO). This enzyme is the major determinant of tryptophan levels in vivo. Acetaminophen administration (100mg/kg for three hours) was shown to significantly inhibit (p<0.05) the activity of TDO, indicating increased peripheral levels of tryptophan. This experiment was followed up with determination of brain serotonin and pineal melatonin. Brain serotonin was determined using the ELISA technique. Melatonin was estimated using this technique as well as with pineal organ culture. Acetaminophen administration (100mg/kg for three hours) significantly increased (p<0.05) brain serotonin levels. Using organ culture where exogenous (3H) tryptophan is metabolised to (3H) melatonin, acetaminophen (100mg/kg for three hours) was shown to significantly increase (p<0.05) pineal melatonin concentrations. However, the ELISA technique did not reveal any changes in endogenous pineal melatonin levels. The final experiment was the determination of urinary 5-hydroxyindole acetic acid (5- HIAA), the major metabolite of serotonin, following acetaminophen administration (100mg/kg for three hours). Acetaminophen was shown to significantly reduce 5-HIAA levels (p<0.05) suggesting reduced catabolism of serotonin. The findings of this study indicate that acetaminophen mimics the actions of an antidepressant. This compelling finding has important clinical implications, and needs to be examined further.
- Full Text:
- Date Issued: 2000
Stability of prochlorperazine in solution and in the solid-state
- Authors: Antunes, Edith Martins
- Date: 2000
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4536 , http://hdl.handle.net/10962/d1016399
- Description: Prochlorperazine, a member of the piperazine subclass of phenothiazines, widely used as an anti-emetic, is susceptible to oxidation to sulfoxides. These are main metabolites and degradants of all phenothiazines which are found to be inactive at the dopamine receptors. Prochlorperazine causes photosensitivity effects in patients attributed to dechlorination at C2 with the release of HCI (Huang and Sands, 1967; Nejmeh and Pilpel, 1978; Moore and Tamat, 1980). The aim of this study is to investigate the thermal and photostability of prochlorperazine edisylate and mesylate salts in the solid state and in solution. Prochlorperazine is available as a fine chemical and in a variety of dosage forms, including injectables and tablets. According to ICH guidelines, any degradants greater than 0.1 % are required to be isolated and identified. In order to assess the photostability of the two salts, an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection, quantitation and ruggedness. Sulfoxides were synthesised for use as standards in the rate studies according to the well-known hydrogen peroxide method (Owens et al., 1989). The rate of prochlorperazine degradation in solution under various light sources (254 nm UV light, diffuse light and sunlight) was studied. The light sources used abovF were quantified using potassium ferrioxalate as a chemical actinometer). The photodegradation rate was found to be greater in ampoules sealed under nitrogen than air, but the thermal degradation was faster in ampoules sealed with air than those purged with nitrogen. Amber ampoules retarded the rate of degradation under all photolytic conditions. This is a vital consideration for the packaging and storage of prochlorperazine in injectables. Degradation was found to occur mainly by first-order kinetics and the degradation rate decreased in the following order: sunlight » UV light 254 nm > fluorescent I diffuse light. Solid state samples, however, were found to be relatively stable to the various light / heat conditions over a 6 month period when compared to prochlorperazine solutions, but still considerably unstable. Thus both storage and packaging is a vital consideration for prochlorperazine injectables. The thermal behaviour of mixtures of prochlorperazine with standard excipients, was assessed for potential interactions, using differential scanning calorimetry. For most of the excipients (magnesium stearate, stearic acid, Explotab®, AC-Di-Sol®, Encompress® and Ludipress®, lactose and Starch 1500®) disappearance or broadening of the melting endotherm of the drug indicated interactions. Lubritab®, however, was the only 'inert' excipient tested. Liquid chromatography - mass spectrometry (LC-MS) was used to determine the nature of the degradation products. The major degradation pathways included dechlorination and demethylation of the parent drug, as well as sulfoxidation and Noxidation. Prochlorperazine underwent dechlorination and sulfoxidation with subsequent photosubstitution to yield the 2-hydroxy derivative. The solid state photostudies showed the formation of dealkylated, oxidised and hydroxylated products, sulfoxides and dimers. Since N-demethylation, N-oxidation, sulfoxidation and aromatic hydroxylation are reported to occur in the in vitro metabolism of perazine derivatives, it does appear that there is some relationship between metabolites and photoproducts (Breyer, 1974). This study has been successful in providing understanding of the photolytic and thermal degradation pathways of prochlorperazine.
- Full Text:
- Date Issued: 2000
- Authors: Antunes, Edith Martins
- Date: 2000
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4536 , http://hdl.handle.net/10962/d1016399
- Description: Prochlorperazine, a member of the piperazine subclass of phenothiazines, widely used as an anti-emetic, is susceptible to oxidation to sulfoxides. These are main metabolites and degradants of all phenothiazines which are found to be inactive at the dopamine receptors. Prochlorperazine causes photosensitivity effects in patients attributed to dechlorination at C2 with the release of HCI (Huang and Sands, 1967; Nejmeh and Pilpel, 1978; Moore and Tamat, 1980). The aim of this study is to investigate the thermal and photostability of prochlorperazine edisylate and mesylate salts in the solid state and in solution. Prochlorperazine is available as a fine chemical and in a variety of dosage forms, including injectables and tablets. According to ICH guidelines, any degradants greater than 0.1 % are required to be isolated and identified. In order to assess the photostability of the two salts, an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection, quantitation and ruggedness. Sulfoxides were synthesised for use as standards in the rate studies according to the well-known hydrogen peroxide method (Owens et al., 1989). The rate of prochlorperazine degradation in solution under various light sources (254 nm UV light, diffuse light and sunlight) was studied. The light sources used abovF were quantified using potassium ferrioxalate as a chemical actinometer). The photodegradation rate was found to be greater in ampoules sealed under nitrogen than air, but the thermal degradation was faster in ampoules sealed with air than those purged with nitrogen. Amber ampoules retarded the rate of degradation under all photolytic conditions. This is a vital consideration for the packaging and storage of prochlorperazine in injectables. Degradation was found to occur mainly by first-order kinetics and the degradation rate decreased in the following order: sunlight » UV light 254 nm > fluorescent I diffuse light. Solid state samples, however, were found to be relatively stable to the various light / heat conditions over a 6 month period when compared to prochlorperazine solutions, but still considerably unstable. Thus both storage and packaging is a vital consideration for prochlorperazine injectables. The thermal behaviour of mixtures of prochlorperazine with standard excipients, was assessed for potential interactions, using differential scanning calorimetry. For most of the excipients (magnesium stearate, stearic acid, Explotab®, AC-Di-Sol®, Encompress® and Ludipress®, lactose and Starch 1500®) disappearance or broadening of the melting endotherm of the drug indicated interactions. Lubritab®, however, was the only 'inert' excipient tested. Liquid chromatography - mass spectrometry (LC-MS) was used to determine the nature of the degradation products. The major degradation pathways included dechlorination and demethylation of the parent drug, as well as sulfoxidation and Noxidation. Prochlorperazine underwent dechlorination and sulfoxidation with subsequent photosubstitution to yield the 2-hydroxy derivative. The solid state photostudies showed the formation of dealkylated, oxidised and hydroxylated products, sulfoxides and dimers. Since N-demethylation, N-oxidation, sulfoxidation and aromatic hydroxylation are reported to occur in the in vitro metabolism of perazine derivatives, it does appear that there is some relationship between metabolites and photoproducts (Breyer, 1974). This study has been successful in providing understanding of the photolytic and thermal degradation pathways of prochlorperazine.
- Full Text:
- Date Issued: 2000
An evaluation of recirculating artificial stream designs for acute toxicity testing using two South African Ephemeroptera species exposed to sodium sulphate
- Authors: Binder, Markus
- Date: 2000
- Subjects: Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5690 , http://hdl.handle.net/10962/d1005376 , Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
- Description: Three artificial stream designs, termed Large Artificial Stream Units (LASUs), Raceways, and Channels, at two major scales (1700 L, 12.5 L and 20 L recirculated volume) were developed at the Institute for Water Research, Rhodes University, Grahamstown, in order to explore the possibilities of using indigenous rheophilic macroinvertebrates in routine toxicity tests. This study compared these systems, using 96h-EC50 values from sodium sulphate toxicity tests as the experimental response. Two local Ephemeroptera (Leptophlebiidae: Adenophlebia auriculata Eaton, and Baetidae: Afroptilum sudafricanum Lestage) were evaluated for their suitability in routine toxicity tests; and the possible effects of elevated salinity levels in South African rivers on the test species were assessed. Two sets of experiments with each mayfly species were conducted, following an unreplicated regression design. Dechlorinated tap water was used as the water source. Experiments in the Channels were repeated to determine experimental variability. Results were compared statistically by testing for overlap of 95% confidence limits (95%Cls) of EC50 values. The differences between A. auriculata EC50 values in the different systems were statistically significant (no overlap of 95%CLs), but they were not more variable than has been considered normal for biological systems (Coefficient of variation 20.1 %; ratio of greatest EC50 / smallest EC50 1.63). The differences were not related to the scale or the average current velocity characteristic of each stream design (average current velocity LASUs - Raceways - Channels 0.090 - 0.083 - 0.038 m/s). The Channels proved to be most efficient with regard to practical performance as they are portable and easily transportable, user-friendly, reliable, splash-free, cost effective to construct, and can easily be adapted to specific requirements. These systems are therefore recommended for regular use. The suitability of the two mayfly species for routine toxicity testing was evaluated. A. auriculata EC50 values showed a significant negative correlation with the corresponding average body-size (range 1476 - 1610 μm, mean 1555 μm). The different average body-sizes probably reflected the abundance of a certain size range present in the Palmiet River at the time of collection. Both species reacted similarly to Na₂S0₄ (similar slopes of the toxicity curves), identifying this salt as a slow acting toxicant. A. sudafricanum populations were more sensitive to Na₂S0₄ (EC50 3.404 g/L) than A. auriculata (EC50 8.090 g/L), probably because of its smaller body-size (mean 709 μm) and a lack of extremely tolerant individuals. In comparison to other freshwater macro invertebrates, including the standard toxicity test organism Daphnia spp., both mayfly species seemed to be moderately tolerant of Na₂S0₄; therefore there was no particular advantage to using these indigenous taxa rather than Daphnia spp. An assessment of the effects of elevated salinity/TDS levels on the test taxa yielded preliminary insights. A NaCI-EC50 for A. sudafricanum could be extrapolated and suggested a higher sensitivity to Na₂S0₄ than to NaCl. When Na₂S0₄ EC50 values of both species were compared to selected TDS levels of South African rivers, 4. auriculata would mostly not be affected, but A. sudafricanum might occasionally suffer from sub-lethal effects, depending on the sulphate proportion of the TDS. The South African guideline for TDS seemed to protect both species sufficiently.
- Full Text:
- Date Issued: 2000
- Authors: Binder, Markus
- Date: 2000
- Subjects: Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5690 , http://hdl.handle.net/10962/d1005376 , Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
- Description: Three artificial stream designs, termed Large Artificial Stream Units (LASUs), Raceways, and Channels, at two major scales (1700 L, 12.5 L and 20 L recirculated volume) were developed at the Institute for Water Research, Rhodes University, Grahamstown, in order to explore the possibilities of using indigenous rheophilic macroinvertebrates in routine toxicity tests. This study compared these systems, using 96h-EC50 values from sodium sulphate toxicity tests as the experimental response. Two local Ephemeroptera (Leptophlebiidae: Adenophlebia auriculata Eaton, and Baetidae: Afroptilum sudafricanum Lestage) were evaluated for their suitability in routine toxicity tests; and the possible effects of elevated salinity levels in South African rivers on the test species were assessed. Two sets of experiments with each mayfly species were conducted, following an unreplicated regression design. Dechlorinated tap water was used as the water source. Experiments in the Channels were repeated to determine experimental variability. Results were compared statistically by testing for overlap of 95% confidence limits (95%Cls) of EC50 values. The differences between A. auriculata EC50 values in the different systems were statistically significant (no overlap of 95%CLs), but they were not more variable than has been considered normal for biological systems (Coefficient of variation 20.1 %; ratio of greatest EC50 / smallest EC50 1.63). The differences were not related to the scale or the average current velocity characteristic of each stream design (average current velocity LASUs - Raceways - Channels 0.090 - 0.083 - 0.038 m/s). The Channels proved to be most efficient with regard to practical performance as they are portable and easily transportable, user-friendly, reliable, splash-free, cost effective to construct, and can easily be adapted to specific requirements. These systems are therefore recommended for regular use. The suitability of the two mayfly species for routine toxicity testing was evaluated. A. auriculata EC50 values showed a significant negative correlation with the corresponding average body-size (range 1476 - 1610 μm, mean 1555 μm). The different average body-sizes probably reflected the abundance of a certain size range present in the Palmiet River at the time of collection. Both species reacted similarly to Na₂S0₄ (similar slopes of the toxicity curves), identifying this salt as a slow acting toxicant. A. sudafricanum populations were more sensitive to Na₂S0₄ (EC50 3.404 g/L) than A. auriculata (EC50 8.090 g/L), probably because of its smaller body-size (mean 709 μm) and a lack of extremely tolerant individuals. In comparison to other freshwater macro invertebrates, including the standard toxicity test organism Daphnia spp., both mayfly species seemed to be moderately tolerant of Na₂S0₄; therefore there was no particular advantage to using these indigenous taxa rather than Daphnia spp. An assessment of the effects of elevated salinity/TDS levels on the test taxa yielded preliminary insights. A NaCI-EC50 for A. sudafricanum could be extrapolated and suggested a higher sensitivity to Na₂S0₄ than to NaCl. When Na₂S0₄ EC50 values of both species were compared to selected TDS levels of South African rivers, 4. auriculata would mostly not be affected, but A. sudafricanum might occasionally suffer from sub-lethal effects, depending on the sulphate proportion of the TDS. The South African guideline for TDS seemed to protect both species sufficiently.
- Full Text:
- Date Issued: 2000
Distributed authentication for resource control
- Authors: Burdis, Keith Robert
- Date: 2000
- Subjects: Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4630 , http://hdl.handle.net/10962/d1006512 , Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Description: This thesis examines distributed authentication in the process of controlling computing resources. We investigate user sign-on and two of the main authentication technologies that can be used to control a resource through authentication and providing additional security services. The problems with the existing sign-on scenario are that users have too much credential information to manage and are prompted for this information too often. Single Sign-On (SSO) is a viable solution to this problem if physical procedures are introduced to minimise the risks associated with its use. The Generic Security Services API (GSS-API) provides security services in a manner in- dependent of the environment in which these security services are used, encapsulating security functionality and insulating users from changes in security technology. The un- derlying security functionality is provided by GSS-API mechanisms. We developed the Secure Remote Password GSS-API Mechanism (SRPGM) to provide a mechanism that has low infrastructure requirements, is password-based and does not require the use of long-term asymmetric keys. We provide implementations of the Java GSS-API bindings and the LIPKEY and SRPGM GSS-API mechanisms. The Secure Authentication and Security Layer (SASL) provides security to connection- based Internet protocols. After finding deficiencies in existing SASL mechanisms we de- veloped the Secure Remote Password SASL mechanism (SRP-SASL) that provides strong password-based authentication and countermeasures against known attacks, while still be- ing simple and easy to implement. We provide implementations of the Java SASL binding and several SASL mechanisms, including SRP-SASL.
- Full Text:
- Date Issued: 2000
- Authors: Burdis, Keith Robert
- Date: 2000
- Subjects: Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4630 , http://hdl.handle.net/10962/d1006512 , Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Description: This thesis examines distributed authentication in the process of controlling computing resources. We investigate user sign-on and two of the main authentication technologies that can be used to control a resource through authentication and providing additional security services. The problems with the existing sign-on scenario are that users have too much credential information to manage and are prompted for this information too often. Single Sign-On (SSO) is a viable solution to this problem if physical procedures are introduced to minimise the risks associated with its use. The Generic Security Services API (GSS-API) provides security services in a manner in- dependent of the environment in which these security services are used, encapsulating security functionality and insulating users from changes in security technology. The un- derlying security functionality is provided by GSS-API mechanisms. We developed the Secure Remote Password GSS-API Mechanism (SRPGM) to provide a mechanism that has low infrastructure requirements, is password-based and does not require the use of long-term asymmetric keys. We provide implementations of the Java GSS-API bindings and the LIPKEY and SRPGM GSS-API mechanisms. The Secure Authentication and Security Layer (SASL) provides security to connection- based Internet protocols. After finding deficiencies in existing SASL mechanisms we de- veloped the Secure Remote Password SASL mechanism (SRP-SASL) that provides strong password-based authentication and countermeasures against known attacks, while still be- ing simple and easy to implement. We provide implementations of the Java SASL binding and several SASL mechanisms, including SRP-SASL.
- Full Text:
- Date Issued: 2000
Minimal motion capture with inverse kinematics for articulated human figure animation
- Authors: Casanueva, Luis
- Date: 2000
- Subjects: Virtual reality , Image processing -- Digital techniques
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4620 , http://hdl.handle.net/10962/d1006485 , Virtual reality , Image processing -- Digital techniques
- Description: Animating an articulated figure usually requires expensive hardware in terms of motion capture equipment, processing power and rendering power. This implies a high cost system and thus eliminates the use of personal computers to drive avatars in virtual environments. We propose a system to animate an articulated human upper body in real-time, using minimal motion capture trackers to provide position and orientation for the limbs. The system has to drive an avatar in a virtual environment on a low-end computer. The cost of the motion capture equipment must be relatively low (hence the use of minimal trackers). We discuss the various types of motion capture equipment and decide to use electromagnetic trackers which are adequate for our requirements while being reasonably priced. We also discuss the use of inverse kinematics to solve for the articulated chains making up the topology of the articulated figure. Furthermore, we offer a method to describe articulated chains as well as a process to specify the reach of up to four link chains with various levels of redundancy for use in articulated figures. We then provide various types of constraints to reduce the redundancy of non-defined articulated chains, specifically for chains found in an articulated human upper body. Such methods include a way to solve for the redundancy in the orientation of the neck link, as well as three different methods to solve the redundancy of the articulated human arm. The first method involves eliminating a degree of freedom from the chain, thus reducing its redundancy. The second method calculates the elevation angle of the elbow position from the elevation angle of the hand. The third method determines the actual position of the elbow from an average of previous positions of the elbow according to the position and orientation of the hand. The previous positions of the elbow are captured during the calibration process. The redundancy of the neck is easily solved due to the small amount of redundancy in the chain. When solving the arm, the first method which should give a perfect result in theory, gives a poor result in practice due to the limitations of both the motion capture equipment and the design. The second method provides an adequate result for the position of the redundant elbow in most cases although fails in some cases. Still it benefits from a simple approach as well as very little need for calibration. The third method provides the most accurate method of the three for the position of the redundant elbow although it also fails in some cases. This method however requires a long calibration session for each user. The last two methods allow for the calibration data to be used in latter session, thus reducing considerably the calibration required. In combination with a virtual reality system, these processes allow for the real-time animation of an articulated figure to drive avatars in virtual environments or for low quality animation on a low-end computer.
- Full Text:
- Date Issued: 2000
- Authors: Casanueva, Luis
- Date: 2000
- Subjects: Virtual reality , Image processing -- Digital techniques
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4620 , http://hdl.handle.net/10962/d1006485 , Virtual reality , Image processing -- Digital techniques
- Description: Animating an articulated figure usually requires expensive hardware in terms of motion capture equipment, processing power and rendering power. This implies a high cost system and thus eliminates the use of personal computers to drive avatars in virtual environments. We propose a system to animate an articulated human upper body in real-time, using minimal motion capture trackers to provide position and orientation for the limbs. The system has to drive an avatar in a virtual environment on a low-end computer. The cost of the motion capture equipment must be relatively low (hence the use of minimal trackers). We discuss the various types of motion capture equipment and decide to use electromagnetic trackers which are adequate for our requirements while being reasonably priced. We also discuss the use of inverse kinematics to solve for the articulated chains making up the topology of the articulated figure. Furthermore, we offer a method to describe articulated chains as well as a process to specify the reach of up to four link chains with various levels of redundancy for use in articulated figures. We then provide various types of constraints to reduce the redundancy of non-defined articulated chains, specifically for chains found in an articulated human upper body. Such methods include a way to solve for the redundancy in the orientation of the neck link, as well as three different methods to solve the redundancy of the articulated human arm. The first method involves eliminating a degree of freedom from the chain, thus reducing its redundancy. The second method calculates the elevation angle of the elbow position from the elevation angle of the hand. The third method determines the actual position of the elbow from an average of previous positions of the elbow according to the position and orientation of the hand. The previous positions of the elbow are captured during the calibration process. The redundancy of the neck is easily solved due to the small amount of redundancy in the chain. When solving the arm, the first method which should give a perfect result in theory, gives a poor result in practice due to the limitations of both the motion capture equipment and the design. The second method provides an adequate result for the position of the redundant elbow in most cases although fails in some cases. Still it benefits from a simple approach as well as very little need for calibration. The third method provides the most accurate method of the three for the position of the redundant elbow although it also fails in some cases. This method however requires a long calibration session for each user. The last two methods allow for the calibration data to be used in latter session, thus reducing considerably the calibration required. In combination with a virtual reality system, these processes allow for the real-time animation of an articulated figure to drive avatars in virtual environments or for low quality animation on a low-end computer.
- Full Text:
- Date Issued: 2000
The solubility enhancement and the stability assessment of rifampicin, isoniazid and pyrazinamide in aqueous media
- Authors: Chen, Yu-Jen
- Date: 2000
- Subjects: Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4346 , http://hdl.handle.net/10962/d1005009 , Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Description: Tuberculosis (TB) is a highly contagious disease caused by the bacterium known as Mycobacterium tuberculosis which is widely spread in South Africa, especially in the rural areas of the Western Province. Rifampicin, isoniazid and pyrazinamide are the three most effective drugs against this organism. However, most of the current commercial anti-TB formulations are inconvenient to administrate. This results in patient non-compliance which has increased with incomplete tuberculosis treatment and further has intensified the mortality rate. The matter is especially severe amongst the paediatric and geriatric patients. Therefore, creating a "user-friendly" but non-alcoholic liquid formulation should improve the whole situation. The key to a successful formulation relies on sufficient concentrations of the drugs within the formulation together with acceptable stability of these drugs. Therefore, during the pre-formulation stage, the solubility and stability studies of rifampicin, isoniazid and pyrazinamide are to be conducted. Rifampicin, isoniazid and pyrazinamide were fully characterized and identified by means of spectroscopic and thermal techniques. A HPLC method for simultaneous analysis of the three drugs was developed and validated. This HPLC method was employed for all the solubility and stability assessments. Unbuffered HPLC water of pH value 7.01 was chosen as the aqueous solvent. This was decided after the stability of rifampicin, isoniazid and pyrazinamide was studied at a pH range of 2 to 10. The solubility and the stability studies of rifampicin, isoniazid, pyrazinamide, rifampicin with isoniazid, rifampicin with pyrazinamide, isoniazid with pyrazinamide and rifampicin combined with both isoniazid and pyrazinamide were performed in the presence of various agents. These agents can be categorized into three groups: the surfactants (poloxamer 188, poloxamer 407 and sorbitol) which could increase the intrinsic solubility or the drugs by altering the surface tensions of the aqueous solution medium, the suspending agents (carbopol 934 and carbopol 974P) which could enable the amount of dosage required to be homogeneously suspended in the formulation without considering the low intrinsic solubility factor of the drugs, and the complexing agents (ß-cyclodextrin, hydroxypropyl-ß-cyclodextrin and -cyclodextrin) which could initiated the inclusion complex between the host cyclodextrin and the drugs, thus further enhance the solubility of the drugs . The stability assessments were performed after 7-days stability trail with the HPLC method developed. Each drug/combination of drugs were stored in closed ampoules and subjected to 25, 40 and 60° C with or without nitrogen flushing while in the presence of the above mentioned agents. While assessing the solubility/stability of the drugs in the presence of the above mentioned surfactants, the phase-solubility curves indicate that both rifampicin and pyrazinamide fail to achieve the desired concentration. Moreover, the stability-time plots clearly indicate that these surfactants fail to enhance the general stabilities of the drugs. When the stabilizing effects of the above mentioned suspending agents were investigated, it was found that although the desired concentration could be easily accomplished by suspending the drug in the aqueous carbopol solutions, the stabilities of the different drug combinations were still below the regulatory level. Cyclodextrins are well known to form inclusion complexes with less polar drug molecules. The inclusion complexation could enhance both the solubility and the stability of the included drug molecules. The computer force field generated models of the cyclodextrin-drug were used to predict the complexation sites. The results indicated the all the inclusion complexation between the drugs and the cyclodextrins were favourable, but do not necessary protect the potential degradation sites of the drugs. The stability results confirmed the above findings as the cyclodextrins did not enhance the stability of the drugs. Various drug-drug interaction pathways were also predicted from the experimental observations which clearly indicated the stability reductions of these drugs in combination. This leads to the conclusion that a liquid formulation combining rifampicin, isoniazid and pyrazinamide should not initiate the use of aqueous solutions as the protic ions of the solution are able to initiate the degradation of these drugs.
- Full Text:
- Date Issued: 2000
- Authors: Chen, Yu-Jen
- Date: 2000
- Subjects: Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4346 , http://hdl.handle.net/10962/d1005009 , Gel permeation chromatography , Rifampin , Isoniazid , Pyridazines
- Description: Tuberculosis (TB) is a highly contagious disease caused by the bacterium known as Mycobacterium tuberculosis which is widely spread in South Africa, especially in the rural areas of the Western Province. Rifampicin, isoniazid and pyrazinamide are the three most effective drugs against this organism. However, most of the current commercial anti-TB formulations are inconvenient to administrate. This results in patient non-compliance which has increased with incomplete tuberculosis treatment and further has intensified the mortality rate. The matter is especially severe amongst the paediatric and geriatric patients. Therefore, creating a "user-friendly" but non-alcoholic liquid formulation should improve the whole situation. The key to a successful formulation relies on sufficient concentrations of the drugs within the formulation together with acceptable stability of these drugs. Therefore, during the pre-formulation stage, the solubility and stability studies of rifampicin, isoniazid and pyrazinamide are to be conducted. Rifampicin, isoniazid and pyrazinamide were fully characterized and identified by means of spectroscopic and thermal techniques. A HPLC method for simultaneous analysis of the three drugs was developed and validated. This HPLC method was employed for all the solubility and stability assessments. Unbuffered HPLC water of pH value 7.01 was chosen as the aqueous solvent. This was decided after the stability of rifampicin, isoniazid and pyrazinamide was studied at a pH range of 2 to 10. The solubility and the stability studies of rifampicin, isoniazid, pyrazinamide, rifampicin with isoniazid, rifampicin with pyrazinamide, isoniazid with pyrazinamide and rifampicin combined with both isoniazid and pyrazinamide were performed in the presence of various agents. These agents can be categorized into three groups: the surfactants (poloxamer 188, poloxamer 407 and sorbitol) which could increase the intrinsic solubility or the drugs by altering the surface tensions of the aqueous solution medium, the suspending agents (carbopol 934 and carbopol 974P) which could enable the amount of dosage required to be homogeneously suspended in the formulation without considering the low intrinsic solubility factor of the drugs, and the complexing agents (ß-cyclodextrin, hydroxypropyl-ß-cyclodextrin and -cyclodextrin) which could initiated the inclusion complex between the host cyclodextrin and the drugs, thus further enhance the solubility of the drugs . The stability assessments were performed after 7-days stability trail with the HPLC method developed. Each drug/combination of drugs were stored in closed ampoules and subjected to 25, 40 and 60° C with or without nitrogen flushing while in the presence of the above mentioned agents. While assessing the solubility/stability of the drugs in the presence of the above mentioned surfactants, the phase-solubility curves indicate that both rifampicin and pyrazinamide fail to achieve the desired concentration. Moreover, the stability-time plots clearly indicate that these surfactants fail to enhance the general stabilities of the drugs. When the stabilizing effects of the above mentioned suspending agents were investigated, it was found that although the desired concentration could be easily accomplished by suspending the drug in the aqueous carbopol solutions, the stabilities of the different drug combinations were still below the regulatory level. Cyclodextrins are well known to form inclusion complexes with less polar drug molecules. The inclusion complexation could enhance both the solubility and the stability of the included drug molecules. The computer force field generated models of the cyclodextrin-drug were used to predict the complexation sites. The results indicated the all the inclusion complexation between the drugs and the cyclodextrins were favourable, but do not necessary protect the potential degradation sites of the drugs. The stability results confirmed the above findings as the cyclodextrins did not enhance the stability of the drugs. Various drug-drug interaction pathways were also predicted from the experimental observations which clearly indicated the stability reductions of these drugs in combination. This leads to the conclusion that a liquid formulation combining rifampicin, isoniazid and pyrazinamide should not initiate the use of aqueous solutions as the protic ions of the solution are able to initiate the degradation of these drugs.
- Full Text:
- Date Issued: 2000
Physiological, perceptual and other performance decrements in combat related tasks following prolonged heavy-load marching
- Authors: Clark, Lisa Anne
- Date: 2000
- Subjects: Performance -- Psychological aspects , Performance standards -- Case studies , Exercise -- Physiological aspects , Exercise -- Psychological aspects , Marching -- Physiological aspects , Soldiers -- Job stress
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5130 , http://hdl.handle.net/10962/d1005209 , Performance -- Psychological aspects , Performance standards -- Case studies , Exercise -- Physiological aspects , Exercise -- Psychological aspects , Marching -- Physiological aspects , Soldiers -- Job stress
- Description: In response to challenging situations physiological and psychological adaptations result in elevated levels of arousal and when these levels are 'optimal' performance is enhanced. There are however, limitations to the amount of physiological and mental stimulation one can tolerate, with cumulative fatigue effects being the outcome when stressful conditions are imposed on the individual over an extended period of time. As a result of the extreme physical and cognitive demands placed on military forces while in combat, with soldiers being thrust into battle and required to make critical life-or-death determining decisions followed by appropriate motor responses, the physical and psychological capabilities of the troops are pushed to maximal limits, often resulting in undesirable decrements in physical and mental performance, with consequential human and materiel losses. Thirty-two soldiers participated in a battery of combat-related field and laboratory tests, first under 'normal' conditions with no prior physical activity and then immediately after the participation of an intensive bout of exercise. Physiological and perceptual responses plus standard of performance were measured at various stages of testing. Results of the Rating of Perceived Exertion (RPE), Body Discomfort Scale and heart rate responses revealed significantly higher levels of psychophysical strai,n in response to the strenuous physical activity. Despite these findings, the electromyographic (EMG) activity and efficiency of the combat-related skills were not negatively affected. Rather, nominal improvements in post-activity performance were noted, specifically response time, and this was attributed to elevated arousal and activation as a result of the exercise that was of sufficient duration to enhance arousal without imposing long term cumulative fatigue effects.
- Full Text:
- Date Issued: 2000
- Authors: Clark, Lisa Anne
- Date: 2000
- Subjects: Performance -- Psychological aspects , Performance standards -- Case studies , Exercise -- Physiological aspects , Exercise -- Psychological aspects , Marching -- Physiological aspects , Soldiers -- Job stress
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5130 , http://hdl.handle.net/10962/d1005209 , Performance -- Psychological aspects , Performance standards -- Case studies , Exercise -- Physiological aspects , Exercise -- Psychological aspects , Marching -- Physiological aspects , Soldiers -- Job stress
- Description: In response to challenging situations physiological and psychological adaptations result in elevated levels of arousal and when these levels are 'optimal' performance is enhanced. There are however, limitations to the amount of physiological and mental stimulation one can tolerate, with cumulative fatigue effects being the outcome when stressful conditions are imposed on the individual over an extended period of time. As a result of the extreme physical and cognitive demands placed on military forces while in combat, with soldiers being thrust into battle and required to make critical life-or-death determining decisions followed by appropriate motor responses, the physical and psychological capabilities of the troops are pushed to maximal limits, often resulting in undesirable decrements in physical and mental performance, with consequential human and materiel losses. Thirty-two soldiers participated in a battery of combat-related field and laboratory tests, first under 'normal' conditions with no prior physical activity and then immediately after the participation of an intensive bout of exercise. Physiological and perceptual responses plus standard of performance were measured at various stages of testing. Results of the Rating of Perceived Exertion (RPE), Body Discomfort Scale and heart rate responses revealed significantly higher levels of psychophysical strai,n in response to the strenuous physical activity. Despite these findings, the electromyographic (EMG) activity and efficiency of the combat-related skills were not negatively affected. Rather, nominal improvements in post-activity performance were noted, specifically response time, and this was attributed to elevated arousal and activation as a result of the exercise that was of sufficient duration to enhance arousal without imposing long term cumulative fatigue effects.
- Full Text:
- Date Issued: 2000
Strike comparison of the compositional variations of the lower group and middle group chromitite seams of the critical zone, Western Bushveld complex
- Authors: Doig, Heather Leslie
- Date: 2000
- Subjects: Chromite -- South Africa , Geology -- South Africa , Mineralogy -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5005 , http://hdl.handle.net/10962/d1005618
- Description: The variations in the composition, specifically the Cr20 S content and the Cr:Fe ratio, and the morphology of the Lower Group (LG) and Middle Group (MG) chromitite seams of the Critical Zone (CZ) across the western Bushveld Complex, including the Ruighoek and Brits sections, is investigated by means of whole-rock chemical data, both major and trace elements analysis, XRD and electron microprobe data. As a result ofthe paucity of exposed or developed LG1 - LG5 chromitite seams in the western Bushveld Complex, this study is confined to the investigation of the compositional variations of the LG6 to MG4 chromitite seams. In only one section, the Ruighoek section, was the entire succession of chromitite seams, from the LG1 - MG4, exposed. The silicate host rocks from the LG6 pyroxenite footwall to the collar of the CC2 drillcore (lower uCZ) in the Rustenburg section were sampled. This study reviews the compositional trends of the silicate host rocks, as the compositional variations of the chromitite seams reflect the chemical evolution of the host cumulate environment and, to a lesser degree, the composition onhe interstitial mineral phases in the chromitite seams. The compositional variations of the LG and MG chromitite seams are attributed to the compositional contrast between the replenishing magma and the resident magma. The chemical trends of the LG and MG chromitite layers and the host cumUlate rOCKS do not support the existence of two compositionalfy dissimilar magmas in the CZ, rather the cyclic layering of the CZ and the chemical variations of the chromitite seams are attributed to the mixing of primitive magma with the resident magma, both of which have essentially similar compositions. The compositional variations of the LG and MG chromitite seams along strike away from the supposed feeder site (Union section) to the distal facies (Brits section) are attributed to the advanced compositional contrast between the resident magma and the replenishing primitive magma pulses. The CZ is characterized by reversals in fractionation trends and this is attributed to the compositional evolution of the parental magma and not to the replenishment of the resident magma by influxes of grossly dissimilar magma compositions. The Cr20 S content and the Cr:Fe ratio of the MG chromitite layers increase from the Ruighoek (near proximal) section to the Brits section (distal facies). This is attributed to the advanced compositional contrasts between the resident magma and the replenishing primitive magma. In contrast, the Cr20 3 content and Cr:Fe ratios ofthe LG6 and LG8a chromitite seams decreases eastwards from the Ruighoek section. The average Cr:Fe ratio for the western Bushveld Complex is between 1.5 and\2.0, nonetheless, a progressively lower Cr:Fe ratio is noted from the LG1 chromitite up through to the MG4 chromitite seam in the Ruighoek section. tn the LG2 - LG4 chromitite interval a deviation to higher.lratios is encountered. A progressive substitution of Cr by AT and Fe in the Cr-spinel crystal lattice characterizes the chromitite succession from the LG1 seam up through the chromitite succession to MG4. The petrogeneSiS of the chromitite seams of the CZ is attributed to magma mixing and fractional crystallization of a single magma type.
- Full Text:
- Date Issued: 2000
- Authors: Doig, Heather Leslie
- Date: 2000
- Subjects: Chromite -- South Africa , Geology -- South Africa , Mineralogy -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5005 , http://hdl.handle.net/10962/d1005618
- Description: The variations in the composition, specifically the Cr20 S content and the Cr:Fe ratio, and the morphology of the Lower Group (LG) and Middle Group (MG) chromitite seams of the Critical Zone (CZ) across the western Bushveld Complex, including the Ruighoek and Brits sections, is investigated by means of whole-rock chemical data, both major and trace elements analysis, XRD and electron microprobe data. As a result ofthe paucity of exposed or developed LG1 - LG5 chromitite seams in the western Bushveld Complex, this study is confined to the investigation of the compositional variations of the LG6 to MG4 chromitite seams. In only one section, the Ruighoek section, was the entire succession of chromitite seams, from the LG1 - MG4, exposed. The silicate host rocks from the LG6 pyroxenite footwall to the collar of the CC2 drillcore (lower uCZ) in the Rustenburg section were sampled. This study reviews the compositional trends of the silicate host rocks, as the compositional variations of the chromitite seams reflect the chemical evolution of the host cumulate environment and, to a lesser degree, the composition onhe interstitial mineral phases in the chromitite seams. The compositional variations of the LG and MG chromitite seams are attributed to the compositional contrast between the replenishing magma and the resident magma. The chemical trends of the LG and MG chromitite layers and the host cumUlate rOCKS do not support the existence of two compositionalfy dissimilar magmas in the CZ, rather the cyclic layering of the CZ and the chemical variations of the chromitite seams are attributed to the mixing of primitive magma with the resident magma, both of which have essentially similar compositions. The compositional variations of the LG and MG chromitite seams along strike away from the supposed feeder site (Union section) to the distal facies (Brits section) are attributed to the advanced compositional contrast between the resident magma and the replenishing primitive magma pulses. The CZ is characterized by reversals in fractionation trends and this is attributed to the compositional evolution of the parental magma and not to the replenishment of the resident magma by influxes of grossly dissimilar magma compositions. The Cr20 S content and the Cr:Fe ratio of the MG chromitite layers increase from the Ruighoek (near proximal) section to the Brits section (distal facies). This is attributed to the advanced compositional contrasts between the resident magma and the replenishing primitive magma. In contrast, the Cr20 3 content and Cr:Fe ratios ofthe LG6 and LG8a chromitite seams decreases eastwards from the Ruighoek section. The average Cr:Fe ratio for the western Bushveld Complex is between 1.5 and\2.0, nonetheless, a progressively lower Cr:Fe ratio is noted from the LG1 chromitite up through to the MG4 chromitite seam in the Ruighoek section. tn the LG2 - LG4 chromitite interval a deviation to higher.lratios is encountered. A progressive substitution of Cr by AT and Fe in the Cr-spinel crystal lattice characterizes the chromitite succession from the LG1 seam up through the chromitite succession to MG4. The petrogeneSiS of the chromitite seams of the CZ is attributed to magma mixing and fractional crystallization of a single magma type.
- Full Text:
- Date Issued: 2000
The response of the two interrelated river components, geomorphology and riparian vegetation, to interbasin water transfers in the Orange-Fish-Sundays River Interbasin Transfer Scheme
- Authors: du Plessis, A J E
- Date: 2000
- Subjects: Skoenmakers River (South Africa) , Riparian ecology -- South Africa -- Eastern Cape , Geomorphology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4850 , http://hdl.handle.net/10962/d1005526
- Description: The Skoenmakers River (located in the semi-arid Karoo region of the Eastern Cape) is being used as a transfer route for water transferred by the Orange-Fish-Sundays River Interbasin Transfer Scheme. The change in the hydrological regime of this once ephemeral stream to a much bigger perennial river led to dramatic changes to both the physical structure and riparian vegetation structure of the river system. These changes differ for each of the three river sections, the upper,middle and lower reaches. Qualitative, descriptive geomorphological data was gathered by means of field observations and this was then compared to the quantitative data collected by means of surveyed cross-sectional profiles at selected sites along the length of both the regulated Skoenmakers River and a nonregulated tributary of equivalent size, the Volkers River. Riparian vegetation data was gathered by means of plot sampling along belt transects at each site. A qualitative assessment of the vegetation conditions was also made at each site and then added to the quantitative data from the plot sampling. At each site the different morphological units were identified along the cross-section and changes in the vegetation and sediment composition were recorded. Aerial photographs were used as additional sources of data and observations made from these were compared to data gathered in the field. The pre-IBT channel in this river section was formed by low frequency flood flows but the hydrological regime has now been converted to base flows much higher than normal flood flows. Severe incision, erosion and degradation of both the channel bed and banks occurred. In the lower reaches, post-IBT base flows are lower than pre-IBT flood flows and, due to the increased catchment area, the impact of the IBT was better ‘absorbed’ by the river system. Aggradation and deposition increased for the regulated river in comparison to the non-regulated river due to more sediment introduced The IBT had the greatest impact in the upper reaches of the regulated river due to more sediment introduced at the top of the system.
- Full Text:
- Date Issued: 2000
- Authors: du Plessis, A J E
- Date: 2000
- Subjects: Skoenmakers River (South Africa) , Riparian ecology -- South Africa -- Eastern Cape , Geomorphology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4850 , http://hdl.handle.net/10962/d1005526
- Description: The Skoenmakers River (located in the semi-arid Karoo region of the Eastern Cape) is being used as a transfer route for water transferred by the Orange-Fish-Sundays River Interbasin Transfer Scheme. The change in the hydrological regime of this once ephemeral stream to a much bigger perennial river led to dramatic changes to both the physical structure and riparian vegetation structure of the river system. These changes differ for each of the three river sections, the upper,middle and lower reaches. Qualitative, descriptive geomorphological data was gathered by means of field observations and this was then compared to the quantitative data collected by means of surveyed cross-sectional profiles at selected sites along the length of both the regulated Skoenmakers River and a nonregulated tributary of equivalent size, the Volkers River. Riparian vegetation data was gathered by means of plot sampling along belt transects at each site. A qualitative assessment of the vegetation conditions was also made at each site and then added to the quantitative data from the plot sampling. At each site the different morphological units were identified along the cross-section and changes in the vegetation and sediment composition were recorded. Aerial photographs were used as additional sources of data and observations made from these were compared to data gathered in the field. The pre-IBT channel in this river section was formed by low frequency flood flows but the hydrological regime has now been converted to base flows much higher than normal flood flows. Severe incision, erosion and degradation of both the channel bed and banks occurred. In the lower reaches, post-IBT base flows are lower than pre-IBT flood flows and, due to the increased catchment area, the impact of the IBT was better ‘absorbed’ by the river system. Aggradation and deposition increased for the regulated river in comparison to the non-regulated river due to more sediment introduced The IBT had the greatest impact in the upper reaches of the regulated river due to more sediment introduced at the top of the system.
- Full Text:
- Date Issued: 2000
The use of indigenous macroinvertebrates and Daphnia pulex in acute toxicity testing
- Authors: Everitt, Victoria Jane
- Date: 2000
- Subjects: Water -- Pollution -- Toxicology , Toxicity testing , Daphnia pulex
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5795 , http://hdl.handle.net/10962/d1005483
- Description: Aquatic toxicology has been identified as a valuable tool in the identification and management of chemical pollution in aquatic ecosystems. Standardised methodologies for acute aquatic bioassays have been adopted from international agencies. As a result of these standard methods, the use of laboratory cultured organisms for toxicity testing has been more popular than that of indigenous field-caught organisms. Included in these adopted methods are those for the cultured crustacean Daphnia pUlex. D.pulex is adapted to living in standing water and the suitability of this species to determine toxic effects for South African riverine environments, which are largely flowing, has been questioned. Thus this thesis is a case-study ofthe use of D.pulex and indigenous site-specific macroinvertebrates as toxicity test organisms for setting acute water quality guidelines to protect aquatic ecosystems. The study highlights site-specific problems such as reference sites and organism identification. The acute tolerance of selected indigenous invertebrates was compared to that of D. pulex, using both a single-substance reference toxicant (zinc) and selected whole efiluents. The significance of source population and culture age as a potential source of biological variability between D.pulex cultures was also investigated. D.pulex cultures have been initiated in South Africa from females collected from a number of different local populations; also it is assumed that no genetic change (due to mutation) occurs within a D.pulex culture over time. In order to establish if source population and culture age are a source of biological variability between D.pulex experiments, the acute tolerJuce to zinc of two different D.pulex populations and three different generations within a population were compared. Due to experimental variability results were inconclusive, and differences in tolerance as a result of population difference or culture age could not be determined with confidence. The acute tolerance of D.pulex to a single reference chemical (zinc) and selected whole efiluents was compared to that of selected indigenous invertebrates. Acute 48 h D.pulex zinc tolerance (LC50 range: 0.22 - 0.60 mg/l Zn) was found to be more sensitive than acute 96 h tolerances shown by mayfly species A.fconurus peringueyi (Heptageniidae) (LC50: 17.42 mg/l Zn), Euthrauluselegans (Leptophlebiidae) (LC50: 0.98 mg/IZn), Ba~tidae (LC50: 0.94mg/IZn) and shrimp, Caradina nilotica (Atyidae) (LC50: 3.17 mg/l Zn). This result suggests that guidelines for zinc set using D.pulex will protect the selected indigenous invertebrates. Selected whole eftluents were not acutely toxic to either D.pulex or selected indigenous invertebrates. These experiments were used as a case study for method development regarding the comparative use of D.pulex and indigenous invertebrates in acute whole eftluent toxicity testing. Finally, it is recommended that a suite of indigenous organisms (e.g. macroinvertebrates, fish and algae), as well as laboratory cultured D.pulex, be used in the initial setting of guidelines and that D.pulex be used for routine compliance monitoring. It is futher recommended that a suite of available monitoring methods, such as chemical and biomonitoring methodologies, be used in conjuction with toxicity testing in water quality management.
- Full Text:
- Date Issued: 2000
- Authors: Everitt, Victoria Jane
- Date: 2000
- Subjects: Water -- Pollution -- Toxicology , Toxicity testing , Daphnia pulex
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5795 , http://hdl.handle.net/10962/d1005483
- Description: Aquatic toxicology has been identified as a valuable tool in the identification and management of chemical pollution in aquatic ecosystems. Standardised methodologies for acute aquatic bioassays have been adopted from international agencies. As a result of these standard methods, the use of laboratory cultured organisms for toxicity testing has been more popular than that of indigenous field-caught organisms. Included in these adopted methods are those for the cultured crustacean Daphnia pUlex. D.pulex is adapted to living in standing water and the suitability of this species to determine toxic effects for South African riverine environments, which are largely flowing, has been questioned. Thus this thesis is a case-study ofthe use of D.pulex and indigenous site-specific macroinvertebrates as toxicity test organisms for setting acute water quality guidelines to protect aquatic ecosystems. The study highlights site-specific problems such as reference sites and organism identification. The acute tolerance of selected indigenous invertebrates was compared to that of D. pulex, using both a single-substance reference toxicant (zinc) and selected whole efiluents. The significance of source population and culture age as a potential source of biological variability between D.pulex cultures was also investigated. D.pulex cultures have been initiated in South Africa from females collected from a number of different local populations; also it is assumed that no genetic change (due to mutation) occurs within a D.pulex culture over time. In order to establish if source population and culture age are a source of biological variability between D.pulex experiments, the acute tolerJuce to zinc of two different D.pulex populations and three different generations within a population were compared. Due to experimental variability results were inconclusive, and differences in tolerance as a result of population difference or culture age could not be determined with confidence. The acute tolerance of D.pulex to a single reference chemical (zinc) and selected whole efiluents was compared to that of selected indigenous invertebrates. Acute 48 h D.pulex zinc tolerance (LC50 range: 0.22 - 0.60 mg/l Zn) was found to be more sensitive than acute 96 h tolerances shown by mayfly species A.fconurus peringueyi (Heptageniidae) (LC50: 17.42 mg/l Zn), Euthrauluselegans (Leptophlebiidae) (LC50: 0.98 mg/IZn), Ba~tidae (LC50: 0.94mg/IZn) and shrimp, Caradina nilotica (Atyidae) (LC50: 3.17 mg/l Zn). This result suggests that guidelines for zinc set using D.pulex will protect the selected indigenous invertebrates. Selected whole eftluents were not acutely toxic to either D.pulex or selected indigenous invertebrates. These experiments were used as a case study for method development regarding the comparative use of D.pulex and indigenous invertebrates in acute whole eftluent toxicity testing. Finally, it is recommended that a suite of indigenous organisms (e.g. macroinvertebrates, fish and algae), as well as laboratory cultured D.pulex, be used in the initial setting of guidelines and that D.pulex be used for routine compliance monitoring. It is futher recommended that a suite of available monitoring methods, such as chemical and biomonitoring methodologies, be used in conjuction with toxicity testing in water quality management.
- Full Text:
- Date Issued: 2000
The scrum-down on brain damage effects of cumulative mild head injury in rugby: a comparison of group mean scores between national rugby players and non-contact sport controls
- Authors: Finkelstein, Melissa
- Date: 2000
- Subjects: Sports injuries , Head -- Wounds and injuries , Sports injuries -- Psychological aspects , Neuropsychological tests , Rugby football injuries
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:2976 , http://hdl.handle.net/10962/d1002485 , Sports injuries , Head -- Wounds and injuries , Sports injuries -- Psychological aspects , Neuropsychological tests , Rugby football injuries
- Description: The present study comprises the second phase of a larger and ongoing research study investigating the brain damage effects of cumulative mild head injury in rugby. The purpose of this study was to determine whether cumulative mild head injury sustained in the game of rugby would cause brain injury as evidenced by impaired performance on sensitive neuropsychological tests. Participants were Springbok professional rugby players (n = 26), Under 21 rugby players (n = 19), and a non-contact sport control of national hockey players (n = 21). Comparisons of performance were carried out across a spectrum of neuropsychological tests for the three rugby groups (Total Rugby, Springbok Rugby, and Under 21 Rugby) versus the performance of the non-contact sport control group (Hockey Control), as well as comparisons of performance f9r the subgroups of Rugby Forwards versus Rugby Backs. Comparisons revealed a consistent pattern of poorer performance across all rugby groups relative to the performance of the controls on tests highly sensitive to the effects of diffuse brain damage. Within rugby group comparisons (Forwards versus Backs) showed significantly poorer performance for Total Rugby Forwards and Springbok Rugby Forwards relative to the performance of the respective Total Rugby Backs and Springbok Rugby Backs on sensitive, as well as on somewhat less sensitive, neuropsychological tests. The performance of Under 21 Rugby Forwards relative to Under 21 Rugby Backs demonstrated similar trends. Brain reserve capacity theory was used as a conceptual basis for discussing the implications of these findings.
- Full Text:
- Date Issued: 2000
- Authors: Finkelstein, Melissa
- Date: 2000
- Subjects: Sports injuries , Head -- Wounds and injuries , Sports injuries -- Psychological aspects , Neuropsychological tests , Rugby football injuries
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:2976 , http://hdl.handle.net/10962/d1002485 , Sports injuries , Head -- Wounds and injuries , Sports injuries -- Psychological aspects , Neuropsychological tests , Rugby football injuries
- Description: The present study comprises the second phase of a larger and ongoing research study investigating the brain damage effects of cumulative mild head injury in rugby. The purpose of this study was to determine whether cumulative mild head injury sustained in the game of rugby would cause brain injury as evidenced by impaired performance on sensitive neuropsychological tests. Participants were Springbok professional rugby players (n = 26), Under 21 rugby players (n = 19), and a non-contact sport control of national hockey players (n = 21). Comparisons of performance were carried out across a spectrum of neuropsychological tests for the three rugby groups (Total Rugby, Springbok Rugby, and Under 21 Rugby) versus the performance of the non-contact sport control group (Hockey Control), as well as comparisons of performance f9r the subgroups of Rugby Forwards versus Rugby Backs. Comparisons revealed a consistent pattern of poorer performance across all rugby groups relative to the performance of the controls on tests highly sensitive to the effects of diffuse brain damage. Within rugby group comparisons (Forwards versus Backs) showed significantly poorer performance for Total Rugby Forwards and Springbok Rugby Forwards relative to the performance of the respective Total Rugby Backs and Springbok Rugby Backs on sensitive, as well as on somewhat less sensitive, neuropsychological tests. The performance of Under 21 Rugby Forwards relative to Under 21 Rugby Backs demonstrated similar trends. Brain reserve capacity theory was used as a conceptual basis for discussing the implications of these findings.
- Full Text:
- Date Issued: 2000
The structure and microbiology of floating sulphide oxidising biofilms
- Authors: Gilfillan, Joanne Criseyde
- Date: 2000
- Subjects: Biofilms , Sulfides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3903 , http://hdl.handle.net/10962/d1003962 , Biofilms , Sulfides
- Description: Floating sulphur biofilms are observed as surface layers in numerous aquatic sulphide-rich environments, and apparently play an important role in the cycling of sulphur in its various oxidation states. In addition to the conversion of sulphide to sulphur and/or sulphate species, it has been suspected that subsequent reduction back to sulphide may occur within the floating sulphur biofi1m in organic-rich environments. The use of sulphur biofilms for the harvesting of elemental sulphur from wastewater treatment systems has also been suggested. There is, however, little documented information in the literature on the structure of floating sulphur biofilms, or the microbial species responsible for their occurrence. In this study, floating sulphur biofilms were generated in a continuous flow baflle reactor and their structure was examined using scanning electron microscopy. It was found that they occur as layered structures with morphologically distinct bacterial forms present in different layers of the biofilm. The biofilpl structure was also found to be dynamic, with structural changes observed as feed conditions were altered. An enriched culture derived from the biofi1m demonstrated rates of sulphide oxidation comparable to values reported in the literature for liquid culture systems. The microbiology of the biofi1m was studied using traditional plate culture techniques and analysis ofrRNA genes. Identification of plate culture isolates as representatives of the biofi1m community proved to be limited, leading to a PeR-based cloning approach. The majority of the organisms present in the sulphur biofi1m were classified as species in the genus ~eudomonas, and a number of other bacterial species whose sulphide oxidising capacity has been noted previously. Surprisingly, only 2% of the clone library consisted of Thiobacillus spp., and no sulphate reducing bacteria were identified in the biofilm at all. These results indicate that in organic sulphide-rich environments facultative chemolithoheterotrophic bacterial forms predominate in floating sulphur biofilms, and that the complete biological cycling of sulphur may not occur in these systems.
- Full Text:
- Date Issued: 2000
- Authors: Gilfillan, Joanne Criseyde
- Date: 2000
- Subjects: Biofilms , Sulfides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3903 , http://hdl.handle.net/10962/d1003962 , Biofilms , Sulfides
- Description: Floating sulphur biofilms are observed as surface layers in numerous aquatic sulphide-rich environments, and apparently play an important role in the cycling of sulphur in its various oxidation states. In addition to the conversion of sulphide to sulphur and/or sulphate species, it has been suspected that subsequent reduction back to sulphide may occur within the floating sulphur biofi1m in organic-rich environments. The use of sulphur biofilms for the harvesting of elemental sulphur from wastewater treatment systems has also been suggested. There is, however, little documented information in the literature on the structure of floating sulphur biofilms, or the microbial species responsible for their occurrence. In this study, floating sulphur biofilms were generated in a continuous flow baflle reactor and their structure was examined using scanning electron microscopy. It was found that they occur as layered structures with morphologically distinct bacterial forms present in different layers of the biofilm. The biofilpl structure was also found to be dynamic, with structural changes observed as feed conditions were altered. An enriched culture derived from the biofi1m demonstrated rates of sulphide oxidation comparable to values reported in the literature for liquid culture systems. The microbiology of the biofi1m was studied using traditional plate culture techniques and analysis ofrRNA genes. Identification of plate culture isolates as representatives of the biofi1m community proved to be limited, leading to a PeR-based cloning approach. The majority of the organisms present in the sulphur biofi1m were classified as species in the genus ~eudomonas, and a number of other bacterial species whose sulphide oxidising capacity has been noted previously. Surprisingly, only 2% of the clone library consisted of Thiobacillus spp., and no sulphate reducing bacteria were identified in the biofilm at all. These results indicate that in organic sulphide-rich environments facultative chemolithoheterotrophic bacterial forms predominate in floating sulphur biofilms, and that the complete biological cycling of sulphur may not occur in these systems.
- Full Text:
- Date Issued: 2000
Feeding biology of three euphausiid species in the vicinity of the Prince Edward Archipelago (Southern Ocean)
- Authors: Gurney, Leigh Josephine
- Date: 2000
- Subjects: Euphausiacea , Euphausiacea -- Feeding and feeds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5695 , http://hdl.handle.net/10962/d1005381 , Euphausiacea , Euphausiacea -- Feeding and feeds
- Description: The feeding biology of three euphausiid species, Euphausia vallentini (adults and juveniles), E. longirostris and Nematoscelis megalops was investigated during austral autumn (April/May) of 1998 and 1999, in the vicinity of the Prince Edward Islands (Southern Ocean). Data on the abundance and biomass of these species, estimated from bongo net tows, were investigated. Trophic position was assessed using gut contents and stable nitrogen isotope measurements. Feeding rate and daily carbon ration were estimated using the gut fluorescence and the gut fullness techniques. Vertical migrations into the surface waters at night were found to be strong for Euphausia vallentini adults and juveniles. Associated with these migrations were clear diel feeding patterns. Insufficient data during daylight hours for E. longirostris made it impossible to determine diel feeding patterns, but high feeding activity did occur during dark hours. Nematoscelis megalops did not show any distinct diel feeding pattern, but slightly higher gut fullness indices in the late afternoon suggested that feeding activity may have been highest during this period. For both Euphausia spp. high gut pigment levels were recorded in 1999, which corresponded to higher ambient chlorophyll a concentrations for that year. Highest initial gut pigment levels and highest ingestion rates were found for Euphausia longirostris in both years and lowest values were observed for N. megalops. High phytoplankton and low metazoan contributions to the diet of Euphausia vallentini juveniles, as shown in the gut content analysis, and low stable nitrogen isotope ratios (ð¹⁵N = 1.39±0.31), both indicated that this group was principally herbivorous. The results of gut content analysis of the adults of E. vallentini were similar to those of the juveniles, however, stable nitrogen isotope results showed that there was a higher degree of omnivory (ð¹⁵N = 3.81±0.66). Daily ration estimates from the gut fluorescence and fullness techniques showed that between 3.3 and 25.7 % of E. vallentini adults total daily carbon ration was derived from autotrophic sources. Although the contribution of carnivory to the diet was difficult to determine, the adults of this species may be considered omnivorous. Irrespective of the degree of carnivory, a dietry shift with an increase in size was evident for this species. Gut content analysis for Euphausia longirostris showed that this species consumed large amounts of both phytoplankton and metazoan prey and this was reflected in the stable nitrogen isotope results (ð¹⁵N = 6.88±0.60). These findings were supported by the results of the daily carbon ration estimates which showed that autotrophic carbon contributed between 6.9 and 20.3 % of the daily carbon consumption. The gut content analysis suggested that N. megalops was omnivorous, and the stable nitrogen isotope results place it in a trophic position equivalent to that of E. longirostris (ð¹⁵N = 6.83±0.78). Calculations from daily ration estimates suggested that only 3.1 % in 1998, and 3.2 % in 1999, of the carbon ingested was of autotrophic origin. This species may therefore be considered carnivorous. Implications of the findings of this study are discussed in terms of carbon cycling in the Southern Ocean.
- Full Text:
- Date Issued: 2000
- Authors: Gurney, Leigh Josephine
- Date: 2000
- Subjects: Euphausiacea , Euphausiacea -- Feeding and feeds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5695 , http://hdl.handle.net/10962/d1005381 , Euphausiacea , Euphausiacea -- Feeding and feeds
- Description: The feeding biology of three euphausiid species, Euphausia vallentini (adults and juveniles), E. longirostris and Nematoscelis megalops was investigated during austral autumn (April/May) of 1998 and 1999, in the vicinity of the Prince Edward Islands (Southern Ocean). Data on the abundance and biomass of these species, estimated from bongo net tows, were investigated. Trophic position was assessed using gut contents and stable nitrogen isotope measurements. Feeding rate and daily carbon ration were estimated using the gut fluorescence and the gut fullness techniques. Vertical migrations into the surface waters at night were found to be strong for Euphausia vallentini adults and juveniles. Associated with these migrations were clear diel feeding patterns. Insufficient data during daylight hours for E. longirostris made it impossible to determine diel feeding patterns, but high feeding activity did occur during dark hours. Nematoscelis megalops did not show any distinct diel feeding pattern, but slightly higher gut fullness indices in the late afternoon suggested that feeding activity may have been highest during this period. For both Euphausia spp. high gut pigment levels were recorded in 1999, which corresponded to higher ambient chlorophyll a concentrations for that year. Highest initial gut pigment levels and highest ingestion rates were found for Euphausia longirostris in both years and lowest values were observed for N. megalops. High phytoplankton and low metazoan contributions to the diet of Euphausia vallentini juveniles, as shown in the gut content analysis, and low stable nitrogen isotope ratios (ð¹⁵N = 1.39±0.31), both indicated that this group was principally herbivorous. The results of gut content analysis of the adults of E. vallentini were similar to those of the juveniles, however, stable nitrogen isotope results showed that there was a higher degree of omnivory (ð¹⁵N = 3.81±0.66). Daily ration estimates from the gut fluorescence and fullness techniques showed that between 3.3 and 25.7 % of E. vallentini adults total daily carbon ration was derived from autotrophic sources. Although the contribution of carnivory to the diet was difficult to determine, the adults of this species may be considered omnivorous. Irrespective of the degree of carnivory, a dietry shift with an increase in size was evident for this species. Gut content analysis for Euphausia longirostris showed that this species consumed large amounts of both phytoplankton and metazoan prey and this was reflected in the stable nitrogen isotope results (ð¹⁵N = 6.88±0.60). These findings were supported by the results of the daily carbon ration estimates which showed that autotrophic carbon contributed between 6.9 and 20.3 % of the daily carbon consumption. The gut content analysis suggested that N. megalops was omnivorous, and the stable nitrogen isotope results place it in a trophic position equivalent to that of E. longirostris (ð¹⁵N = 6.83±0.78). Calculations from daily ration estimates suggested that only 3.1 % in 1998, and 3.2 % in 1999, of the carbon ingested was of autotrophic origin. This species may therefore be considered carnivorous. Implications of the findings of this study are discussed in terms of carbon cycling in the Southern Ocean.
- Full Text:
- Date Issued: 2000
The presence and role of arbuscular mycorrhizal fungi in coastal sand dune systems
- Authors: Haller, Anjanette H. A
- Date: 2000
- Subjects: Mycorrhizas , Sand dune ecology -- South Africa , Mycorrhizal fungi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4196 , http://hdl.handle.net/10962/d1003765 , Mycorrhizas , Sand dune ecology -- South Africa , Mycorrhizal fungi
- Description: Arbuscular mycorrhizas (AM) are mutually beneficial symbiotic associations between the roots of plants and certain Zygomycetous fungi. The role of AM fungi in coastal sand dunes has been explored in many parts of the world, though little work has been conducted in South African dune systems. This study aimed to investigate the presence and extent of mycorrhizal colonisation of a coastal sand dune in South Africa. The roots of five plant species (Scaevola plumieri, Arctotheca populifolia, Ipomoea pes-caprae, Ehrharta villosa and Chrysanthemoides monilifera) were sampled along a foredune profile at Old Woman's River in the Eastern Cape. These roots were assessed for the percentage mycorrhizal colonisation they supported. Spores extracted from the rhizosphere sand of each plant species were counted and identified to genus level. Results were related to seasonality and the position of the plants along the profile. All plant species were found to be mycorrhizal. Percentage colonisation ranged from 0-92%, depending on plant species and season. Mycorrhizal colonisation was generally highest in the winter months, and especially so in I pes-caprae and E. villosa. The extent of various mycorrhizal structures in root tissue varied between plant species. Spore numbers ranged from 0-48 spores 100g-1 sand with highest numbers occurring in winter. S. plumieri and A. populifolia were associated with greatest spore abundance. Four fungal genera (Glomus, Acaulospora, Scutellospora and Gigaspora) were identified. Distribution of these genera showed seasonal variations between plant species. A bioassay, using Sorghum, was conducted to test the inoculum potentials of sand from the Scaevola hummock and the IpomoealEhrharta dune. Highest percentage colonisation occurred in plants grown in the Scaevola sand, which also had the lowest root and shoot measurements. The bioassay confirmed that AM propagules are present and viable, even in the mobile sand of the foredune. This study showed that mycorrhizal colonisation and spore numbers varied seasonally, but that the extent of this was dependent on plant species. The position of plants along the foredune profile tended to be less important than plant species. It is thought that the growth cycle and rooting system of each plant species determines seasonal cycles and abundance of AM fungi. Variation within fungal populations probably also impacts on this. Knowledge of the presence and distribution of AM fungi in this system paves the way for more detailed studies which need to examine the role of these endophytes in South African sand dunes.
- Full Text:
- Date Issued: 2000
- Authors: Haller, Anjanette H. A
- Date: 2000
- Subjects: Mycorrhizas , Sand dune ecology -- South Africa , Mycorrhizal fungi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4196 , http://hdl.handle.net/10962/d1003765 , Mycorrhizas , Sand dune ecology -- South Africa , Mycorrhizal fungi
- Description: Arbuscular mycorrhizas (AM) are mutually beneficial symbiotic associations between the roots of plants and certain Zygomycetous fungi. The role of AM fungi in coastal sand dunes has been explored in many parts of the world, though little work has been conducted in South African dune systems. This study aimed to investigate the presence and extent of mycorrhizal colonisation of a coastal sand dune in South Africa. The roots of five plant species (Scaevola plumieri, Arctotheca populifolia, Ipomoea pes-caprae, Ehrharta villosa and Chrysanthemoides monilifera) were sampled along a foredune profile at Old Woman's River in the Eastern Cape. These roots were assessed for the percentage mycorrhizal colonisation they supported. Spores extracted from the rhizosphere sand of each plant species were counted and identified to genus level. Results were related to seasonality and the position of the plants along the profile. All plant species were found to be mycorrhizal. Percentage colonisation ranged from 0-92%, depending on plant species and season. Mycorrhizal colonisation was generally highest in the winter months, and especially so in I pes-caprae and E. villosa. The extent of various mycorrhizal structures in root tissue varied between plant species. Spore numbers ranged from 0-48 spores 100g-1 sand with highest numbers occurring in winter. S. plumieri and A. populifolia were associated with greatest spore abundance. Four fungal genera (Glomus, Acaulospora, Scutellospora and Gigaspora) were identified. Distribution of these genera showed seasonal variations between plant species. A bioassay, using Sorghum, was conducted to test the inoculum potentials of sand from the Scaevola hummock and the IpomoealEhrharta dune. Highest percentage colonisation occurred in plants grown in the Scaevola sand, which also had the lowest root and shoot measurements. The bioassay confirmed that AM propagules are present and viable, even in the mobile sand of the foredune. This study showed that mycorrhizal colonisation and spore numbers varied seasonally, but that the extent of this was dependent on plant species. The position of plants along the foredune profile tended to be less important than plant species. It is thought that the growth cycle and rooting system of each plant species determines seasonal cycles and abundance of AM fungi. Variation within fungal populations probably also impacts on this. Knowledge of the presence and distribution of AM fungi in this system paves the way for more detailed studies which need to examine the role of these endophytes in South African sand dunes.
- Full Text:
- Date Issued: 2000
The implementation of a core architecture for geophysical data acquisition
- Authors: Heasman, Ray Edward
- Date: 2000
- Subjects: Geophysics -- Data processing , Computer software -- Development , Seismometers , Computer input-output equipment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5471 , http://hdl.handle.net/10962/d1005256 , Geophysics -- Data processing , Computer software -- Development , Seismometers , Computer input-output equipment
- Description: This thesis describes the design, development and implementation of the core hardware and software of a modular data acquisition system for geophysical data collection. The primary application for this system is the acquisition and realtime processing of seismic data captured in mines. This system will be used by a commercial supplier of seismic instrumentation, ISS International, as a base architecture for the development of future products. The hardware and software has been designed to be extendable and support distributed processing. The IEEE-1394 High Performance Serial Bus is used to communicate with other CPU modules or peripherals. The software includes a pre-emptive multitasking microkernel, an asynchronous mailbox-based message passing communications system, and a functional IEEE-1394 protocol stack. The reasons for the end design and implementation decisions are given, and the problems encountered in the development of this system are described. A critical assessment of the match between the requirements for the project and the functionality of the implementation is made.
- Full Text:
- Date Issued: 2000
- Authors: Heasman, Ray Edward
- Date: 2000
- Subjects: Geophysics -- Data processing , Computer software -- Development , Seismometers , Computer input-output equipment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5471 , http://hdl.handle.net/10962/d1005256 , Geophysics -- Data processing , Computer software -- Development , Seismometers , Computer input-output equipment
- Description: This thesis describes the design, development and implementation of the core hardware and software of a modular data acquisition system for geophysical data collection. The primary application for this system is the acquisition and realtime processing of seismic data captured in mines. This system will be used by a commercial supplier of seismic instrumentation, ISS International, as a base architecture for the development of future products. The hardware and software has been designed to be extendable and support distributed processing. The IEEE-1394 High Performance Serial Bus is used to communicate with other CPU modules or peripherals. The software includes a pre-emptive multitasking microkernel, an asynchronous mailbox-based message passing communications system, and a functional IEEE-1394 protocol stack. The reasons for the end design and implementation decisions are given, and the problems encountered in the development of this system are described. A critical assessment of the match between the requirements for the project and the functionality of the implementation is made.
- Full Text:
- Date Issued: 2000
Aspects of the ecology and reproductive biology of the limpet, Helcion pruinosus (Gastropoda : prosobranchia)
- Authors: Henninger, Tony Oskar
- Date: 2000
- Subjects: Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5641 , http://hdl.handle.net/10962/d1005323 , Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Description: Helcion pruinosus, the rayed limpet, is found in the midshore region of the intertidal zone, (i.e. the Balanoid zone) of rocky shores, from Saldanha Bay to Sodwana Bay along the coast of South Africa. At Gonubie (32°57'S/25°01'E) this species of limpet was found under boulders, (when not feeding), and could reach average densities of 85/ m². The limpets prefer smooth boulders, avoiding those encrusted by coralline algae or boulders with a rough texture. There was no habitat segregation between adult and juvenile H. pruinosus, i.e. there was no sign of up-shore migration by larger individuals. Males out-numbered females by, on average 1.4 : 1, which was a similar sex ratio to that of the congeneric species, H. pectunculus (Gray, 996). Unlike H. pectunculus, there were no differences in shell lengths between males and females (p = 0.946 at Gonubie, south-east coast and p = 0.961 at Kommetjie, south-west coast; t-test). Shell height could also not be used as a criterion to differentiate between the sexes. The average maximum shell length of H. pruinosus at Gonubie and Kommetjie was 25 mm, but the maximum shell lengths found were 30 mm, (one individual in each case), on both the southeast coast and west coast. Growth occurred most rapidly in the first year of life, with individuals reaching 15 mm after 1 year. In the second year limpet growth slowed to only 7 mm. Sexual maturity was reached at a shell length of between 11 to 14 mm (at an age of 8 months to 1 year). The life-span of H. pruinosus was determined at 2.55 years on the south-east coast and 2.9 years on the south-west coast. Micro-growth bands were produced tidally. Growth occurred allometrically, i.e. shell length increased at a faster rate than shell height. The limpets foraged during low tide, at night, presumably feeding on epilithic algae on the boulders. A second smaller peak of limpet activity was often recorded during the day, when low tide coincided with dawn). More limpets (up to ten times more) were active at spring tides compared to neap tides. Limpet activity was greatest during the spring tides of autumn. During all seasons limpet activity peaked 30 minutes before low water, after which numbers decreased rapidly. All limpets had retreated beneath the boulders before being covered by the flooding tide. It was concluded that the limpets were responding to both endogenous and exogenous cues, but the actual stimulus for retreat could not be determined. The limpets did not return to a fixed scar nor did they return rigidly to a home site. H. pruinosus was found to be gonochoristic. Sexes could be separated, on dissection, according to the colour of their gonads (males had white gonads, whilst that of the females was olive-green). Gonads were present throughout the year in most individuals, i.e. totally spent animals were never observed. Reproductive seasonality was similar in west coast and south-east coast animals. The gonad indices of the west coast limpets were higher, (maximum of 35%), compared to that on the southeast coast, (25%). The animals were probably trickle spawners, with some individuals liberating gametes throughout the year. There was however synchrony in gametogenesis between male and female limpets on both the west coast and south-east coast lines. Gonad indices peaked in the summer months (October to December) with a second minor peak in April/May. These peaks occurred before the release of the gametes in spawning events. The gonad index was lowest in winter, (July). The ovaries were full of mature eggs (oocytes having a diameter of 200 to 250 ~) prior to spawning. The acinal wall thickness had been decreasing prior to spawning. After spawning there was an increase in previtellogenic eggs « 100 μm) in females, and an increase in the acinal wall thickness to indicate spermatogenesis. The two populations are subjected to different environmental conditions and the actual cue for stimulating the release of gametes could not be determined. Finally, a table of differences between H pruinosus and its sister species, H pectunculus was created to show the life-style of H pruinosus.
- Full Text:
- Date Issued: 2000
- Authors: Henninger, Tony Oskar
- Date: 2000
- Subjects: Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5641 , http://hdl.handle.net/10962/d1005323 , Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Description: Helcion pruinosus, the rayed limpet, is found in the midshore region of the intertidal zone, (i.e. the Balanoid zone) of rocky shores, from Saldanha Bay to Sodwana Bay along the coast of South Africa. At Gonubie (32°57'S/25°01'E) this species of limpet was found under boulders, (when not feeding), and could reach average densities of 85/ m². The limpets prefer smooth boulders, avoiding those encrusted by coralline algae or boulders with a rough texture. There was no habitat segregation between adult and juvenile H. pruinosus, i.e. there was no sign of up-shore migration by larger individuals. Males out-numbered females by, on average 1.4 : 1, which was a similar sex ratio to that of the congeneric species, H. pectunculus (Gray, 996). Unlike H. pectunculus, there were no differences in shell lengths between males and females (p = 0.946 at Gonubie, south-east coast and p = 0.961 at Kommetjie, south-west coast; t-test). Shell height could also not be used as a criterion to differentiate between the sexes. The average maximum shell length of H. pruinosus at Gonubie and Kommetjie was 25 mm, but the maximum shell lengths found were 30 mm, (one individual in each case), on both the southeast coast and west coast. Growth occurred most rapidly in the first year of life, with individuals reaching 15 mm after 1 year. In the second year limpet growth slowed to only 7 mm. Sexual maturity was reached at a shell length of between 11 to 14 mm (at an age of 8 months to 1 year). The life-span of H. pruinosus was determined at 2.55 years on the south-east coast and 2.9 years on the south-west coast. Micro-growth bands were produced tidally. Growth occurred allometrically, i.e. shell length increased at a faster rate than shell height. The limpets foraged during low tide, at night, presumably feeding on epilithic algae on the boulders. A second smaller peak of limpet activity was often recorded during the day, when low tide coincided with dawn). More limpets (up to ten times more) were active at spring tides compared to neap tides. Limpet activity was greatest during the spring tides of autumn. During all seasons limpet activity peaked 30 minutes before low water, after which numbers decreased rapidly. All limpets had retreated beneath the boulders before being covered by the flooding tide. It was concluded that the limpets were responding to both endogenous and exogenous cues, but the actual stimulus for retreat could not be determined. The limpets did not return to a fixed scar nor did they return rigidly to a home site. H. pruinosus was found to be gonochoristic. Sexes could be separated, on dissection, according to the colour of their gonads (males had white gonads, whilst that of the females was olive-green). Gonads were present throughout the year in most individuals, i.e. totally spent animals were never observed. Reproductive seasonality was similar in west coast and south-east coast animals. The gonad indices of the west coast limpets were higher, (maximum of 35%), compared to that on the southeast coast, (25%). The animals were probably trickle spawners, with some individuals liberating gametes throughout the year. There was however synchrony in gametogenesis between male and female limpets on both the west coast and south-east coast lines. Gonad indices peaked in the summer months (October to December) with a second minor peak in April/May. These peaks occurred before the release of the gametes in spawning events. The gonad index was lowest in winter, (July). The ovaries were full of mature eggs (oocytes having a diameter of 200 to 250 ~) prior to spawning. The acinal wall thickness had been decreasing prior to spawning. After spawning there was an increase in previtellogenic eggs « 100 μm) in females, and an increase in the acinal wall thickness to indicate spermatogenesis. The two populations are subjected to different environmental conditions and the actual cue for stimulating the release of gametes could not be determined. Finally, a table of differences between H pruinosus and its sister species, H pectunculus was created to show the life-style of H pruinosus.
- Full Text:
- Date Issued: 2000
Mesozooplankton community structure in the vicinity of the Prince Edward Islands (Southern Ocean) 37⁰ 50'E, 46⁰ 45'S
- Authors: Hunt, Brian Peter Vere
- Date: 2000
- Subjects: Zooplankton , Zooplankton -- Prince Edward Islands , Phytoplankton , Chlorophyll
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5732 , http://hdl.handle.net/10962/d1005418 , Zooplankton , Zooplankton -- Prince Edward Islands , Phytoplankton , Chlorophyll
- Description: Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May), 1996 to 1999. Each year zooplankton samples were collected with a bongo net (300 µm mesh) at stations upstream (west), between and downstream (east) of the islands. Chlorophyll a concentrations were determined fluorometrically, corresponding with each net tow. The positions of the Subantarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands in the upstream region, were determined by a line of CTD and/or XBT stations. Both the SAF and the APF were characterised by a high degree of meridional variation in position. Changes in position of the fronts were shown to occur very rapidly. In 1999 the APF moved southwards by ~40nm and the SAF northwards by ~60nm in a period of two weeks, while in 1996 the SAF appeared to move ~120nm northwards in a two week period. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, through the alteration of local flow dynamics. Water retention in 1996, associated with the location of the SAF and APF far to the north and south of the PEIs respectively, corresponded with high chlorophyll a concentrations in the inter-island region (reaching 1.54 mg.m^(-3)). When the fronts were close to the islands, in 1997 and 1999, and a flow through environment existed, chlorophyll a concentrations in the inter-island region were comparatively low. Although biomass enhancement was only observed at the SAF in 1996, phytoplankton size structure in 1999 indicated that, when close to the PEIs, frontal production may be transported to the island system. This is potentially an important source of allochthonous input into the island system. Zooplankton assemblages were a mix of sub-Antarctic and Antarctic communities, with a weak presence of sub-tropical species. Cluster analysis showed that during each survey the region in the vicinity of the PEIs was divided into different, spatially separated zooplankton communities, associated with water masses of different origins. These communities were identified by variations in the abundance and biomass of species rather than variation in species composition and, in general, there was a relatively high degree of similarity both within and between surveys. Inter-annual community analysis revealed that, in many cases, there was greater similarity between communities from different years than communities within years, indicating that short-term variability exceeded inter-annual variability. Multiple regression analysis showed that the major correlate with zooplankton community structure during all surveys was sea temperature, accounting for as much as 77% of the variation in community structure. Temperature was indicative of the relative contribution of sub-Antarctic and Antarctic communities, with low temperatures being characterised by an increased predominance of Antarctic communities and vice versa. The differentiation between sub-Antarctic and Antarctic waters, and their respective communities, was particularly pronounced when the SAF and APF were in close proximity to the islands. Surface salinity and sounding had limited effect on community structure. The affect of sounding was intrinsically related to zooplankton interaction with the island ecosystem. Predation by the islands' land based predators and benthic fish appears to decrease zooplankton biomass over the island shelf, particularly the macrozooplankton size fraction. However, this may only be an important factor under conditions of water retention when replenishment of zooplankton stocks is low. The low densities of many macrozooplankton species, and other deep migrators, on the island shelf may be due to their limited advection onto shallow topography. By contrast, there are indications that zooplankton species occurring at shallower depths may be concentrated in the inter-island region by mesoscale flow patterns. Analysis of the population structure of the copepod Calanus simillimus showed that this species occurred at different stages in its life cycle during different years, even though sampling took place in the same calendar months, indicating that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided for a long-term trend of southward movement of the SAF. This may have a significant affect on the PEI ecosystem, increasing the proportion of allochthonous input and altering the tropho-dynamics of the island ecosystem
- Full Text:
- Date Issued: 2000
- Authors: Hunt, Brian Peter Vere
- Date: 2000
- Subjects: Zooplankton , Zooplankton -- Prince Edward Islands , Phytoplankton , Chlorophyll
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5732 , http://hdl.handle.net/10962/d1005418 , Zooplankton , Zooplankton -- Prince Edward Islands , Phytoplankton , Chlorophyll
- Description: Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May), 1996 to 1999. Each year zooplankton samples were collected with a bongo net (300 µm mesh) at stations upstream (west), between and downstream (east) of the islands. Chlorophyll a concentrations were determined fluorometrically, corresponding with each net tow. The positions of the Subantarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands in the upstream region, were determined by a line of CTD and/or XBT stations. Both the SAF and the APF were characterised by a high degree of meridional variation in position. Changes in position of the fronts were shown to occur very rapidly. In 1999 the APF moved southwards by ~40nm and the SAF northwards by ~60nm in a period of two weeks, while in 1996 the SAF appeared to move ~120nm northwards in a two week period. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, through the alteration of local flow dynamics. Water retention in 1996, associated with the location of the SAF and APF far to the north and south of the PEIs respectively, corresponded with high chlorophyll a concentrations in the inter-island region (reaching 1.54 mg.m^(-3)). When the fronts were close to the islands, in 1997 and 1999, and a flow through environment existed, chlorophyll a concentrations in the inter-island region were comparatively low. Although biomass enhancement was only observed at the SAF in 1996, phytoplankton size structure in 1999 indicated that, when close to the PEIs, frontal production may be transported to the island system. This is potentially an important source of allochthonous input into the island system. Zooplankton assemblages were a mix of sub-Antarctic and Antarctic communities, with a weak presence of sub-tropical species. Cluster analysis showed that during each survey the region in the vicinity of the PEIs was divided into different, spatially separated zooplankton communities, associated with water masses of different origins. These communities were identified by variations in the abundance and biomass of species rather than variation in species composition and, in general, there was a relatively high degree of similarity both within and between surveys. Inter-annual community analysis revealed that, in many cases, there was greater similarity between communities from different years than communities within years, indicating that short-term variability exceeded inter-annual variability. Multiple regression analysis showed that the major correlate with zooplankton community structure during all surveys was sea temperature, accounting for as much as 77% of the variation in community structure. Temperature was indicative of the relative contribution of sub-Antarctic and Antarctic communities, with low temperatures being characterised by an increased predominance of Antarctic communities and vice versa. The differentiation between sub-Antarctic and Antarctic waters, and their respective communities, was particularly pronounced when the SAF and APF were in close proximity to the islands. Surface salinity and sounding had limited effect on community structure. The affect of sounding was intrinsically related to zooplankton interaction with the island ecosystem. Predation by the islands' land based predators and benthic fish appears to decrease zooplankton biomass over the island shelf, particularly the macrozooplankton size fraction. However, this may only be an important factor under conditions of water retention when replenishment of zooplankton stocks is low. The low densities of many macrozooplankton species, and other deep migrators, on the island shelf may be due to their limited advection onto shallow topography. By contrast, there are indications that zooplankton species occurring at shallower depths may be concentrated in the inter-island region by mesoscale flow patterns. Analysis of the population structure of the copepod Calanus simillimus showed that this species occurred at different stages in its life cycle during different years, even though sampling took place in the same calendar months, indicating that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided for a long-term trend of southward movement of the SAF. This may have a significant affect on the PEI ecosystem, increasing the proportion of allochthonous input and altering the tropho-dynamics of the island ecosystem
- Full Text:
- Date Issued: 2000
Aspects of reproduction in the four-striped field mouse, Rhabdomys pumilio
- Authors: Jackson, Claire
- Date: 2000
- Subjects: Microtus , Mice , Mice -- Reproduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5637 , http://hdl.handle.net/10962/d1005319 , Microtus , Mice , Mice -- Reproduction
- Description: Rhabdomys pumilio, in the Eastern Cape of South Africa, does not use short day length as an inhibitory cue for reproductive activity, and, despite previous records indicating that these mice are strictly seasonal in their reproduction, litters have been found during the winters of some years,both in the Eastern Cape and in the Western Cape. This led me to believe that the reproductive activity of Rhabdomys pumilio is more opportunistic and that the cue or cues used to control reproduction are less predictable and, or more variable than the photoperiod cue used by many seasonally reproducing rodents. Two experiments were conducted, investigating the influence of low ambient temperature (15⁰C)and reduced food availability on the reproductive activity of both male and female four striped field mice. Mice were maintained in one of four conditions (food restricted at 15⁰C, food restricted at 26⁰C, ad lib. food at 15⁰C, and ad lib. food at 26⁰C) for 4 (males) and 8 weeks (females)(photoperiod 12L:12D, humidity 40%). Results indicated that the males reduced their reproductive activity slightly when exposed to either low temperature or low food availability and that maximum inhibition of reproduction occurred when mice were exposed to both low temperature and low food availability. However, female reproductive activity was inhibited when exposed to low food availability, irrespective of the temperature. Both sexes of mice showed varying abilities to resist fat loss and, in the males, the size of the fat store had a significant effect on reproduction. This varying ability to resist fat loss could be related to levels of activity and in the females (where activity was quantified), high activity scores were significantly associated with reproductive inhibition. These results support the hypothesis that reproduction in Rhabdomys pumilio is opportunistic and controlled by the availability of energy. I propose that the females will be more sensitive to reproductive inhibition due to their far greater post-fertilization responsibilities, where the reproductive activity of the females is rapidly inhibited by a reduction in food availability, while the males are less readily inhibited by low food availability or low temperature, unless the change in the controlling factors is severe enough, or prolonged, at which stage their reproductive activity will cease. The significance of opportunistic reproduction in the seasonal but unpredictable climate of the study area is discussed.
- Full Text:
- Date Issued: 2000
- Authors: Jackson, Claire
- Date: 2000
- Subjects: Microtus , Mice , Mice -- Reproduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5637 , http://hdl.handle.net/10962/d1005319 , Microtus , Mice , Mice -- Reproduction
- Description: Rhabdomys pumilio, in the Eastern Cape of South Africa, does not use short day length as an inhibitory cue for reproductive activity, and, despite previous records indicating that these mice are strictly seasonal in their reproduction, litters have been found during the winters of some years,both in the Eastern Cape and in the Western Cape. This led me to believe that the reproductive activity of Rhabdomys pumilio is more opportunistic and that the cue or cues used to control reproduction are less predictable and, or more variable than the photoperiod cue used by many seasonally reproducing rodents. Two experiments were conducted, investigating the influence of low ambient temperature (15⁰C)and reduced food availability on the reproductive activity of both male and female four striped field mice. Mice were maintained in one of four conditions (food restricted at 15⁰C, food restricted at 26⁰C, ad lib. food at 15⁰C, and ad lib. food at 26⁰C) for 4 (males) and 8 weeks (females)(photoperiod 12L:12D, humidity 40%). Results indicated that the males reduced their reproductive activity slightly when exposed to either low temperature or low food availability and that maximum inhibition of reproduction occurred when mice were exposed to both low temperature and low food availability. However, female reproductive activity was inhibited when exposed to low food availability, irrespective of the temperature. Both sexes of mice showed varying abilities to resist fat loss and, in the males, the size of the fat store had a significant effect on reproduction. This varying ability to resist fat loss could be related to levels of activity and in the females (where activity was quantified), high activity scores were significantly associated with reproductive inhibition. These results support the hypothesis that reproduction in Rhabdomys pumilio is opportunistic and controlled by the availability of energy. I propose that the females will be more sensitive to reproductive inhibition due to their far greater post-fertilization responsibilities, where the reproductive activity of the females is rapidly inhibited by a reduction in food availability, while the males are less readily inhibited by low food availability or low temperature, unless the change in the controlling factors is severe enough, or prolonged, at which stage their reproductive activity will cease. The significance of opportunistic reproduction in the seasonal but unpredictable climate of the study area is discussed.
- Full Text:
- Date Issued: 2000
Possible crosstalk between signal transduction pathways in the induction of differentiation in HT-29 cells
- Authors: Jamie, Hajierah
- Date: 2000
- Subjects: Cellular signal transduction , Cell differentiation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11096 , http://hdl.handle.net/10948/d1019684
- Description: The investigation into the mechanisms by which compounds such as butyrate induce differentiation in HT-29 cells, is lacking. The colonic carcinoma cell line, HT-29, undergoes differentiation induction in the presence of butyrate and acetoacetate. The Caco-2 cell line spontaneously differentiates on contact inhibition. In this study, a signal transduction pathway involving ATP, cAMP, Ca2+ and the transcriptional factor CREB was investigated following suggestions that the energy state of the cell and diffferentiation are linked. The activity of the MAP kinase cascade, including possible crosstalk that may exist between these pathways was determined. The HT-29 cells were exposed to 5 mM acetoacetate, butyrate, DMSO and propionate. The results of this differentiation induction were compared to Caco-2 and HeLa cells, which are cervical carcinoma cells. It was found that ATP levels are decreased on differentiation induction in HT-29 cells, which, in turn affected the cAMP concentrations. Theoretically, the inducers do not have any effect on PDE 4 activity, and may facilitate the interaction between cAMP and PKA. Influx of Ca2+ into the cells was inhibited to a degree by the inducers, which was possibly overcome by crosstalk between the cAMP and Ca2+ pathways. CREB activation, lineage-specific gene expression, ERK activity and c-myc expression were all dependent on both the inducers used and the cell-type. PKA played a major role in CREB activation in acetoacetate- and butyrate -induced HT-29, Caco-2 and HeLa cells, while a2+/Calmodulin-dependent kinases I/IV may have a secondary role. Alkaline phosphatase expression in HeLa cells was independent of CREB. Evidence that crosstalk between the MAP kinase cascade and the REBactivation pathways exist, was illustrated by increased CREB activation on ERK inhibition in acetoacetate- and butyrate-induced HT-29 and HeLa cells. Also, the role that ERK played in the cells differed with inducer and cell-type. The dependence of cmyc expression on c-jun and c-fos, appeared to be differentiation induction- and celltype specific. Results from this study indicate the potential use of acetoacetate and butyrate as anti-cancer compounds.
- Full Text:
- Date Issued: 2000
- Authors: Jamie, Hajierah
- Date: 2000
- Subjects: Cellular signal transduction , Cell differentiation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11096 , http://hdl.handle.net/10948/d1019684
- Description: The investigation into the mechanisms by which compounds such as butyrate induce differentiation in HT-29 cells, is lacking. The colonic carcinoma cell line, HT-29, undergoes differentiation induction in the presence of butyrate and acetoacetate. The Caco-2 cell line spontaneously differentiates on contact inhibition. In this study, a signal transduction pathway involving ATP, cAMP, Ca2+ and the transcriptional factor CREB was investigated following suggestions that the energy state of the cell and diffferentiation are linked. The activity of the MAP kinase cascade, including possible crosstalk that may exist between these pathways was determined. The HT-29 cells were exposed to 5 mM acetoacetate, butyrate, DMSO and propionate. The results of this differentiation induction were compared to Caco-2 and HeLa cells, which are cervical carcinoma cells. It was found that ATP levels are decreased on differentiation induction in HT-29 cells, which, in turn affected the cAMP concentrations. Theoretically, the inducers do not have any effect on PDE 4 activity, and may facilitate the interaction between cAMP and PKA. Influx of Ca2+ into the cells was inhibited to a degree by the inducers, which was possibly overcome by crosstalk between the cAMP and Ca2+ pathways. CREB activation, lineage-specific gene expression, ERK activity and c-myc expression were all dependent on both the inducers used and the cell-type. PKA played a major role in CREB activation in acetoacetate- and butyrate -induced HT-29, Caco-2 and HeLa cells, while a2+/Calmodulin-dependent kinases I/IV may have a secondary role. Alkaline phosphatase expression in HeLa cells was independent of CREB. Evidence that crosstalk between the MAP kinase cascade and the REBactivation pathways exist, was illustrated by increased CREB activation on ERK inhibition in acetoacetate- and butyrate-induced HT-29 and HeLa cells. Also, the role that ERK played in the cells differed with inducer and cell-type. The dependence of cmyc expression on c-jun and c-fos, appeared to be differentiation induction- and celltype specific. Results from this study indicate the potential use of acetoacetate and butyrate as anti-cancer compounds.
- Full Text:
- Date Issued: 2000
Effects of sustained elevated CO2 concentration and Nitrogen nutrition on wheat (Triticum aestivum L. cv Gamtoos)
- Authors: Kgope, Barney Stephen
- Date: 2000
- Subjects: Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4205 , http://hdl.handle.net/10962/d1003774 , Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Description: There is consensus that high CO2 results in enhanced growth and yield for most crop plants. However, most of these studies were carried out in the presence of adequate nutrients, which is also the case in agricultural systems (managed ecosystems). About 20% of the earth’s land mass have sufficiently low levels of nutrients to cause some kind of stress to plants. On the other hand, elevated [CO2] decreases foliar nutrient elements in plants and as a result partitioning of certain nutrient elements in plants is altered. Little data is available on the partitioning of most nutrient elements in plants, and this will definitely impact on growth and yield. To investigate this, wheat (Triticum aestivum L. c.v. Gamtoos) was grown in controlled environment cabinets at 360 and 700 µmol mol -1 CO2. The full Long-Ashton nutrient solution comprising of three-nitrogen concentrations ([N]) viz. (4,6 and 12 mM) was used to water plants everyday. The measurement of net assimilation rate (NAR), stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE), foliar [N], nitrogen use efficiency (NUE) and growth parameters (total plant biomass (TPB), total plant height (TPH), leaf area (LA), shoot and root dry weight) were made 7 days after germination (7 DAG) till the onset of flowering. The increase in nitrogen supply in the order of 4, 6 and 12mM resulted in an increase in NAR, g_s_ , WUE and a decline in E under elevated [CO2]. Under elevated [CO2] NAR was observed to increase during the first two weeks reaching its maximum at 14 DAG, thereafter followed by a decline reaching its maximum at 28 DAG. This was later followed by an increase at 35 DAG onwards. Under elevated [CO2], NAR was increased significantly between the nitrogen regimes during the first (7-14 DAG) and the last two (35-42 DAG) weeks. The response of assimilation as a function of internal [CO2] (Ci), showed a decrease with age at ages 14, 28 and 35 DAG. This negatively affected the initial slope and the CO2 saturated photosynthetic rates under all treatments. This suggest that acclimation may have been as a result of both stomatal and biochemical limitations. All the photosynthetic pigment levels (chl_a_, chl_b_, chl_(a+b)_, and C_(x+c)_ ) increased with an increase in nitrogen supply from 4 to 6mM [N]. A 12mM [N] resulted in a significant decline in the photosynthetic pigment levels compared to a 6mM [N]. Chla remained higher than chlb under all treatments. Also, NAR was seen to increase and decrease concomitantly with the photosynthetic pigment levels. Foliar [N] was seen to decrease with an increase in nitrogen supply from 4 to 6 mM [N] under elevated [CO2] and the effects were adverse under the 4mM [N]. Under the 6mM N regime foliar [N] was positively correlated to NAR for elevated [CO2] grown plants. Similarly, E was positively correlated to foliar [N] under the same conditions. Elevated CO2 and increase in nitrogen supply had a pronounced effect on total plant height (TPH), total plant biomass (TPB), leaf area (LA), shoot and root dry weight and nitrogen use efficiency (NUE). The effects were more pronounced under a 6mM [N] as a result of high NUE. However, under 12mM [N] growth was not as expected as a result of lower NUE. Under all treatments shoot dry weight (SDW) was positively correlated to NUE. Anatomical studies revealed that total leaf and midrib thickness was significantly increased with an increase in nitrogen supply under elevated CO2 to support the larger leaf areas. There were no significant changes in the chloroplast ultrastructure as a result of the increase in nitrogen supply and CO2 enrichment. Starch grain surface area was seen to decline with an increase in nitrogen under both ambient and elevated CO2. Elevated CO2 and increase in nitrogen supply significantly increased total grain dry weight per plant by 47 and 46% respectively under 6 and 12mM [N]. In contrast, the increase was by about 21, 61 and 67% respectively under 4, 6 and 12mM [N] between the CO2 regimes.
- Full Text:
- Date Issued: 2000
- Authors: Kgope, Barney Stephen
- Date: 2000
- Subjects: Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4205 , http://hdl.handle.net/10962/d1003774 , Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Description: There is consensus that high CO2 results in enhanced growth and yield for most crop plants. However, most of these studies were carried out in the presence of adequate nutrients, which is also the case in agricultural systems (managed ecosystems). About 20% of the earth’s land mass have sufficiently low levels of nutrients to cause some kind of stress to plants. On the other hand, elevated [CO2] decreases foliar nutrient elements in plants and as a result partitioning of certain nutrient elements in plants is altered. Little data is available on the partitioning of most nutrient elements in plants, and this will definitely impact on growth and yield. To investigate this, wheat (Triticum aestivum L. c.v. Gamtoos) was grown in controlled environment cabinets at 360 and 700 µmol mol -1 CO2. The full Long-Ashton nutrient solution comprising of three-nitrogen concentrations ([N]) viz. (4,6 and 12 mM) was used to water plants everyday. The measurement of net assimilation rate (NAR), stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE), foliar [N], nitrogen use efficiency (NUE) and growth parameters (total plant biomass (TPB), total plant height (TPH), leaf area (LA), shoot and root dry weight) were made 7 days after germination (7 DAG) till the onset of flowering. The increase in nitrogen supply in the order of 4, 6 and 12mM resulted in an increase in NAR, g_s_ , WUE and a decline in E under elevated [CO2]. Under elevated [CO2] NAR was observed to increase during the first two weeks reaching its maximum at 14 DAG, thereafter followed by a decline reaching its maximum at 28 DAG. This was later followed by an increase at 35 DAG onwards. Under elevated [CO2], NAR was increased significantly between the nitrogen regimes during the first (7-14 DAG) and the last two (35-42 DAG) weeks. The response of assimilation as a function of internal [CO2] (Ci), showed a decrease with age at ages 14, 28 and 35 DAG. This negatively affected the initial slope and the CO2 saturated photosynthetic rates under all treatments. This suggest that acclimation may have been as a result of both stomatal and biochemical limitations. All the photosynthetic pigment levels (chl_a_, chl_b_, chl_(a+b)_, and C_(x+c)_ ) increased with an increase in nitrogen supply from 4 to 6mM [N]. A 12mM [N] resulted in a significant decline in the photosynthetic pigment levels compared to a 6mM [N]. Chla remained higher than chlb under all treatments. Also, NAR was seen to increase and decrease concomitantly with the photosynthetic pigment levels. Foliar [N] was seen to decrease with an increase in nitrogen supply from 4 to 6 mM [N] under elevated [CO2] and the effects were adverse under the 4mM [N]. Under the 6mM N regime foliar [N] was positively correlated to NAR for elevated [CO2] grown plants. Similarly, E was positively correlated to foliar [N] under the same conditions. Elevated CO2 and increase in nitrogen supply had a pronounced effect on total plant height (TPH), total plant biomass (TPB), leaf area (LA), shoot and root dry weight and nitrogen use efficiency (NUE). The effects were more pronounced under a 6mM [N] as a result of high NUE. However, under 12mM [N] growth was not as expected as a result of lower NUE. Under all treatments shoot dry weight (SDW) was positively correlated to NUE. Anatomical studies revealed that total leaf and midrib thickness was significantly increased with an increase in nitrogen supply under elevated CO2 to support the larger leaf areas. There were no significant changes in the chloroplast ultrastructure as a result of the increase in nitrogen supply and CO2 enrichment. Starch grain surface area was seen to decline with an increase in nitrogen under both ambient and elevated CO2. Elevated CO2 and increase in nitrogen supply significantly increased total grain dry weight per plant by 47 and 46% respectively under 6 and 12mM [N]. In contrast, the increase was by about 21, 61 and 67% respectively under 4, 6 and 12mM [N] between the CO2 regimes.
- Full Text:
- Date Issued: 2000